Research ArticleFTIR and Electrical Study of Dysprosium DopedCobalt Ferrite Nanoparticles

Hemaunt Kumar1 Jitendra Pal Singh2 R C Srivastava1

P Negi1 H M Agrawal1 and K Asokan3

1 Department of Physics G B Pant University of Ag amp Technology Pantnagar Uttarakhand-263145 India2Department of Applied Science Krishna Engineering College Mohan Nagar Ghaziabad Uttar Pradesh-201007 India3 Inter University Accelerator Centre New Delhi 110067 India

Correspondence should be addressed to Hemaunt Kumar hvatsalgmailcom

Received 9 January 2014 Revised 7 April 2014 Accepted 7 April 2014 Published 18 May 2014

Academic Editor Tian Xia

Copyright copy 2014 Hemaunt Kumar et al This is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properlycited

We have studied the role of Dy3+ doping on the XRD TEM FTIR and dielectric and electrical properties of CoFe2O4at room

temperature Cubic spinel phase of CoFe2minusxDyxO4 (119909 = 000 005 010 and 015) was synthesized by using different sintering

temperatures (300 500 700 and 900∘C) The two absorption bands ]1and ]

2are observed in Fourier transform infrared

spectroscopy (FTIR) spectra corresponding to the tetrahedral and octahedral sites which show signature of spinel structure ofthe sample For the sample sintered at 300∘C the dielectric constant is almost unchanged with the frequency at the particularconcentrations of 119909 = 000 and 005 Similar result is obtained for the sample sintered at 500∘C (119909 = 010 015) 700∘C (119909 = 005 010and 015) and 900∘C (119909 = 005 010) An increase in the dielectric constant was observed for the undoped cobalt ferrite sintered at500 700 and 900∘CThe values of electrical resistivity of the materials vary from sim105 to 109Ω-cm

1 Introduction

Spinel ferrites have general formula MO Fe2O3where

M is Zn2+ Ni+2 Co+2 and so forth It constitutes animportant class of magnetic materials having several tech-nological applications like spintronics magnetic diagnosticmagnetic drug delivery storage devices electrical gener-ators microwave devices and so forth [1] Nanoferritesexhibit unusual electrical magnetic and optical propertieswhich are sensitive to their structure method of synthe-sis particle size and type of dopant ions These mate-rials crystallize into a cubic closed-packed structure ofoxygen ions The cations occupy two types of interstitialsites known as tetrahedral (A) site and octahedral (B)site The site occupancy is often depicted by the chemicalformula (M2+

1minus120575Fe3+120575)[M2+

120575Fe3+2minus120575

]O2minus4 where the paren-

theses and square brackets denote A and B sites respec-tively M represents a divalent cation and 120575 is inversionparameter [2]

Among spinel ferrites CoFe2O4is an interesting mag-

netic material due to its high coercivity (sim5400Oe) andmoderate saturation magnetization (sim80 emug) as well asremarkable chemical stability and mechanical hardnesswhich make it a good candidate for the recording media[3 4] The coexistence of spontaneous polarization andmagnetization in CoFe

2O4based composite and core shell

nanoparticles is of great importance [5] However synthe-sising composites and core-shell particles is a complicatedtask rather than synthesizing single phase materials Dopingof Zn in the cobalt ferrite matrix leads to the increaseof dielectric constant whereas nickel substitution leads tothe decrement in the dielectric constant [6] The signatureof ferroelectricity in the magnetically ordered Mo-dopedCoFe2O4has been investigated and it shows the coexistence

of both ferroelectricity and magnetic ordering at roomtemperature [7] The effect of La3+ doping on the electricaldielectric and magnetic properties of cobalt ferrite preparedby coprecipitation technique has been investigated [8] and

Hindawi Publishing CorporationJournal of NanoscienceVolume 2014 Article ID 862415 10 pageshttpdxdoiorg1011552014862415

2 Journal of Nanoscience

Table 1 Calculated XRD parameters of the samples CoFe2minus119909

Dy119909O4sintered at 500∘C

Samples Crystallite size(plusmn1 nm)

Lattice parameter(plusmn001 A)

X-ray density(plusmn002 gmcm3)

Specific surface area(plusmn1m2gm)

119909 = 000 22 837 533 51119909 = 005 16 837 544 69119909 = 010 13 836 557 83119909 = 015 11 836 569 96

low values of dielectric constant dielectric loss andmagneticloss could be correlated with better compositional stoichiom-etry and Fe ions concentrationThe structural electrical andmagnetic studies of Gd3+ doped cobalt ferrite nanoparticleswere investigated and these materials show low loss highresistivity and soft magnetic properties due to Gd3+ doping[9]

It was observed that rare earth doped ferrite exhibitsbetter properties however limited solubility of these ions inferrite is a major issue Moreover the solubility limit dependson the method of synthesis [8] In the lanthanide series themagnetic moment varies from 0 (La3+) to 105 120583B (Dy3+) andlanthanide ions can be isotropic or anisotropic due to thelarge variation of the f-electron orbital contribution to themagnetic interaction The magnetic properties of rare earthdoped ferrites are not well understood either in terms of themagnetic moment of the dopant cations or the unpaired f-electrons [10] Among the lanthanide series Dy3+ ion hasthe highest value of magnetic moment which affects themagnetic and electrical properties of the materials Thereare several issues related to the rare earth ions doping inferrites such as limited solubility of rare earth ions and itseffect on the electrical and magnetic properties which arenot well understood Hence the present work is carried outto get an insight of the underlying physics by performingXRD TEM Fourier transform infrared spectroscopy (FTIR)and dielectric and electrical resistivity measurements of Dy3+doped ferrite

2 Experimental

Nanoparticles of dysprosium doped cobalt ferrite weresynthesized by using the chemical route The stoichio-metric amounts of Fe(NO

3)3sdot9H2O Co(NO

3)2sdot6H2O and

Dy(NO3)3sdot5H2O were dissolved in the distilled water In the

aqueous salt solution citric acid solution was added with thecations to citric acid molar ratio of 1 2 The solution washeated at 85∘C under constant magnetic stirring until thesolution got converted into a viscous gel and was allowed tocool at room temperature The cooled gel was dried in anoven at 100∘C for overnight to form the precursor materialThe precursor material was sintered at 300 500 700 and900∘C for 2 hrs to get the nanoparticles of dysprosium dopedcobalt ferrite X-ray diffraction data were collected on BrukerD8 ADVANDEDX-ray diffractometer using Cu K

120572radiation

(120582 = 154178 A) The ferrite powder was pressed into pelletsof 10mm diameter at a presser of 5 ton after mixing withabout 2 by weight of polyvinyl alcohol binderThese pellets

15 30 45 60

Inte

nsity

(au

)

2120579 (deg)

x = 015

x = 010

x = 005

(111) (220)(311)

(222) (400) (422)(511) (440)

x = 000 500∘C

Figure 1 XRD patterns of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp

015) sintered at temperature of 500∘C

were heated in a furnace at 200∘C for 2 hrs These pelletswere polished and coated with silver on both surfaces fordielectric measurements The dielectric properties of thesamples weremeasuredwith anAgilent 4285A precision LCRmeter in the frequency range of 75 kHz to 5MHz Fouriertransform infrared spectroscopy (FTIR) was recorded atroom temperature in the range of 200 to 4000 cmminus1 usingBruker make Vortex 70 spectrometer

3 Results and Discussion

31 XRD Study Figure 1 shows the representative X-raydiffraction patterns of CoFe

2minus119909Dy119909O4(119909 = 000 005 010

and 015) samples sintered at 500∘CThe synthesized samplesexhibit the presence of cubic spinel phase (JCPDS number-03-0864) No impurity phase was detected even for thehighest concentration of Dy3+ (119909 = 015) All the XRD peakscould be indexed to Fd3m space group with cubic symmetryIt is observed that the XRD peaks of the samples appear tobe broadened with increasing Dy3+ concentration The XRDparameters such as crystallite size lattice parameters X-raydensity and specific surface area are tabulated in Table 1The higher concentration of Dy3+ led to lower crystallinityof the all the samples This may be because more dopantconcentration leads to a higher potential barrier thatDy3+ ionhas to overcome for entering the spinel crystal lattice resultingin crystal lattice distortion and local strain [11]

32 TEM Study Few representative transmission electronmicrographs of the dysprosium doped cobalt ferrite nanopar-ticles at the sintering temperature of 700∘C are shownin Figure 2 The average particle sizes are 49 40 43 and37 nm for the concentration of 119909 = 000 005 010 and015 respectively (Table 2) In the present case the particle

Journal of Nanoscience 3

0 20 40 60 80

8

6

4

2

0

Freq

uenc

y co

unt

Particle size (nm)

x = 000

(a)

0 20 40 60 80

18

16

14

12

10

8

6

4

2

0

Freq

uenc

y co

unt

Particle size (nm)

x = 005

(b)

0 20 40 60 80

8

6

4

2

0

Freq

uenc

y co

unt

Particle size (nm)

x = 010

(c)

x = 015

0 20 40 60 80

8

6

4

2

0

Freq

uenc

y co

unt

Particle size (nm)

(d)

Figure 2 TEMmicrographs of CoFe2minus119909

Dy119909O4sintered at 700∘C (a) 119909 = 000 (b) 119909 = 005 (c) 119909 = 010 (d) 119909 = 015

4 Journal of Nanoscience

400 800 1200 1600 2000 2400 2800 3200 3600 4000

3450 cmminus1

3460 cmminus1

2350 cmminus1

2352 cmminus1

2338 cmminus1

3430 cmminus1

3462 cmminus1

2330 cmminus1

1632 cmminus1

1640 cmminus1

1620 cmminus1

1373 cmminus1

1380 cmminus1

1400 cmminus1

1605 cmminus1

Tran

smiss

ion

()

x = 0001393 cmminus1

x = 005

x = 010

1 2

x = 015

300∘C

Wavenumber (cmminus1)

(a)

400 800 1200 1600 2000 2400 2800 3200 3600 4000

Tran

smiss

ion

()

x = 000

x = 005

x = 010

x = 015

500∘C

Wavenumber (cmminus1)

(b)

400 800 1200 1600 2000 2400 2800 3200 3600 4000

Tran

smiss

ion

()

x = 000

x = 005

x = 010

x = 015

700∘C

Wavenumber (cmminus1)

(c)

400 800 1200 1600 2000 2400 2800 3200 3600 4000

Tran

smiss

ion

()

x = 005

x = 010

x = 015

x = 000 900∘C

Wavenumber (cmminus1)

(d)

Figure 3 FTIR spectra of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at different temperatures of (a) 300∘C (b) 500∘C (c) 700∘C

and (d) 900∘C

Table 2 Particle size of samples CoFe2minus119909

Dy119909O4sintered at 700∘C

Samples Particle size (nm)119909 = 000 49119909 = 005 40119909 = 010 43119909 = 015 37

size is more than that of the crystallite size indicating thatthe particles of the synthesized samples consist of severalcrystallites A decreasing trend of particle size was observedwith the increase of Dy3+ concentration Similar behaviour ofparticle size was observed by other workers also [12]

33 FTIR Study FTIR spectra of dysprosium doped cobaltferrite which were synthesized at different sintering tem-peratures (300ndash900∘C) were recorded in the range of 400ndash5000 cmminus1 at room temperature The obtained results areshown in Figures 3(a)ndash3(d) In ferrites the band appearingat the higher wave number (]

1 500ndash600 cmminus1) is assigned

to the tetrahedral complexes while the band appearing atlower wave number (]

2 400ndash450 cmminus1) is assigned to the

octahedral complexesThe higher wave number ]1represents

the vibration of Fe3+ndashO2minus in the sublattice site A while thelower wave number band ]

2represents the trivalent metal-

oxygen vibration at the octahedral B-sites The differencein the ]

1and ]

2band positions is expected because of the

difference in the Fe3+ndashO2minus distance for the octahedral andthe tetrahedral sites [13] It is seen that the FTIR spectra ofthe dysprosium doped cobalt ferrite nanoparticles show noresidual organic compounds and confirm the formation ofthe organic free dysprosium doped cobalt ferrite above thesintering temperature of 500∘C At lower sintering tempera-ture (300∘C) of dysprosiumdoped cobalt ferrite the observedpeak at about 3410 cmminus1 is attributed to the stretchingvibration of the hydroxyl group and the other observed peaksat around 1400 and 1600 cmminus1 are attributed to the symmetricand asymmetric stretching vibration of CO

2groups The

observed peak around 2330ndash2358 cmminus1 is assigned to thealiphatic and aromatic CndashH bond stretching These bandsstart removing for higher sintering temperature due to theevaporation of CO

2[14]The ratio of the line position of FTIR

bands can be determined by [15] ]1]2= (1198701199051198700)radic2 where

119870119905and119870

0are the force constants for theMndashO bonds in tetra-

hedral and octahedral sites respectively Deviation of theratio119870

1199051198700fromunity indicates that the expansion at one site

is not equally compensated by the shrinkage at another siteIn the present case the peak around 800 cmminus1 becomes more

Journal of Nanoscience 5

Table 3 FTIR data of CoFe2minusxDyxO4 samples sintered at 300 500 700 and 900∘C

Samples 300∘C 500∘C 700∘C 900∘C]1(cmminus1) ]

2(cmminus1) ]

1(cmminus1) ]

2(cmminus1) ]

1(cmminus1) ]

2(cmminus1) ]

1(cmminus1) ]

2(cmminus1)

119909 = 000 567 403 553 410 567 410 560 417119909 = 005 574 417 581 411 574 417 581 417119909 = 010 581 424 594 430 584 417 587 424119909 = 015 594 424 595 437 587 424 594 430

Table 4 Dielectric constant of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) at different sintering temperatures

Samples FrequencyDielectric constant (1205761015840) at different sintering temperatures

300∘C 500∘C 700∘C 900∘C

119909 = 000

75 kHz 180 1127 834 3441MHz 177 1370 1017 3855MHz 173 1559 1143 473

119909 = 005

75 kHz 248 391 567 1491MHz 246 273 567 1495MHz 241 242 557 146

119909 = 010

75 kHz 495 293 267 2201MHz 297 282 263 2205MHz 276 274 257 216

119909 = 015

75 kHz 245 160 183 6921MHz 160 151 180 6795MHz 171 146 183 665

and more narrower with increasing sintering temperaturewhich is due to the grain growth of the particles with increasein sintering temperature The band positions of dysprosiumdoped cobalt ferrite sintered at 300∘C are in the range of567 cmminus1 to 594 cmminus1 for ]

1and 403 cmminus1 to 424 cmminus1 for ]

2

The band positions of the samples sintered 500∘C are in therange of 553 cmminus1 to 595 cmminus1 for ]

1and 410 cmminus1 to 437 cmminus1

for ]2 The band positions of the samples sintered 700∘C are

in the range 567 cmminus1 to 587 cmminus1 for ]1and 410 cmminus1 to

424 cmminus1 for ]2 The band positions of the samples sintered

900∘C are in the range of 560 cmminus1 to 594 cmminus1 for ]1and

417 cmminus1 to 430 cmminus1 for ]2 The vibrational band positions

for all the samples are shown in Table 3 It is observed thatsubstitution of Fe3+ by Dy3+ causes shifting of band positions(Fe3+ndashO2minus) towards higher frequency side due to increasedbond length at B-sites and lattice distortionThis also suggeststhe occupancy of Dy3+ at B-sites

34 Dielectric Behaviour The dielectric constant 1205761015840 of dys-prosium doped cobalt (CoFe

2minus119909Dy119909O4) ferrite has been esti-

mated from capacitance 119862 of the pellets using the formulagiven below [16]

1205761015840=

119862119889

1205760119860

(1)

where 119889 is the thickness of the pellets 119860 is the cross-sectional area in m2 and 120576

0is the permittivity of free space

The variation of dielectric constant against frequency fordifferent samples is shown in Figure 4The values of dielectricconstant are shown in Table 4 The dielectric constant of thedysprosium doped cobalt ferrite (CoFe

2minus119909Dy119909O4) in general

decreases with the increase in the frequency However in thepresent case some deviation was observed from this usualbehaviour For the sample sintered at 300∘C the dielectricconstant is almost unchanged with the frequency at theparticular concentrations of 119909 = 000 and 005 Similar resultis obtained for the sample sintered at 500∘C (119909 = 010 015)700∘C (119909 = 005 010 and 015) and 900∘C (119909 = 005 010)An increase in the dielectric constant was observed for theundoped cobalt ferrite sintered at 500 700 and 900∘C Thedecrease of dielectric constant with increasing frequency isdue to the fact that above certain frequency of the electricfield the electron exchange between Fe2+ and Fe3+ ion cannotfollow the variation of electric fieldThe space charge carriersin a dielectric material require a finite time to line up theiraxes parallel to the direction of the applied electric field If thefrequency of the field increases a point is reached when thespace charge carriers cannot cope up with the applied fieldAs a result the dielectric constant of thesematerials decreasesAs the frequency of the field continuously increases at somestage the space charge polarization would barely have started

6 Journal of Nanoscience

0 1 2 3 4

1600

1400

1200

1000

800

600

400

200

5

1100

1000

900

800

700

600

500

400

300

200

700

600

500

400

300

200

500

450

400

350

300

250

200

150

500 x = 000

500 x = 005

500 x = 010

500 x = 015

700 x = 000

700 x = 005

700 x = 010

700 x = 015

900 x = 000

900 x = 005

900 x = 010

900 x = 015

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)

Die

lect

ric co

nsta

nt

Die

lect

ric co

nsta

ntD

iele

ctric

cons

tant

Die

lect

ric co

nsta

nt

300 x = 000

300 x = 005

300 x = 010

300 x = 015

0 1 2 3 4 5

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)times106

times106

times106

times106

Figure 4 Dielectric constant of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at 300 500 700 and 900∘C

Table 5 Dielectric loss tangent (tan 120575) of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) at different sintering temperatures

Samples Frequency Dielectric tangent loss (tan 120575) at different sintering temperatures300∘C 500∘C 700∘C 900∘C

119909 = 000

75 kHz 0037 0045 0034 00281MHz 0005 0158 0151 01595MHz 0001 0072 0067 0118

119909 = 005

75 kHz 0010 179 00005 000021MHz 0001 0253 00002 000015MHz 0001 00136 00001 0001

119909 = 010

75 kHz 2006 0195 0041 000091MHz 0343 0022 000481 000075MHz 0073 0005 0003 00006

119909 = 015

75 kHz 1644 0159 0051 003951MHz 0222 0026 000481 0004565MHz 0142 0001 0003 00107

Journal of Nanoscience 7

700 x = 000

700 x = 005

700 x = 010

700 x = 015

900 x = 000

900 x = 005

900 x = 010

900 x = 015

0 1 2 3 4 5

500 x = 000

500 x = 005

500 x = 010

500 x = 015

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)

300 x = 000

300 x = 005

300 x = 010

300 x = 015

18

15

12

09

06

03

00

018 016

012

008

004

000

015

012

009

006

003

000

20

15

10

05

00

Die

lect

ric lo

ssD

iele

ctric

loss

Die

lect

ric lo

ssD

iele

ctric

loss

0 1 2 3 4 5

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)times106

times106

times106

times106

Figure 5 Dielectric loss in CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at 300 500 700 and 900∘C

Table 6 Electrical resistivity (120588) of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) at different sintering temperatures

Samples Electrical resistivity (Ω-cm) at different sintering temperatures300∘C 500∘C 700∘C 900∘C

119909 = 000 176 times 107

587 times 107

807 times 106

188 times 106

119909 = 005 683 times 107

18 times 105

787 times 108

162 times 109

119909 = 010 626 times 107

631 times 105

495 times 106

116 times 108

119909 = 015 1245 times 107

2568 times 105

2437 times 106

684 times 106

to move before the field reverses and makes virtually nocontribution to the polarization and hence to dielectricThe increase in dielectric constant with frequency may bedue to resonance effect The resonance may arise due tothe matching of the frequency of charge transfer betweenFe2+ harr Fe3+ ions and that of the applied electric fieldSimilar increase in the dielectric constant was obtained forthe La doped cobalt ferrite [8 17 18]The change in dielectricconstant with increasing dysprosium concentration may be

due to the migration of the Fe3+ ions from octahedral site totetrahedral site A similar behaviour was reported in case ofthe nickel substituted CondashZn ferrite [6] It has been reportedthat dielectric properties of materials are sensitive to themethod of synthesis microstructure and crystallite size Inthe present case two factors which have dominant effectare sintering temperature and concentration of dopant ionsAt lower concentration Dy3+ ions are dissolved in spinellattice however at higher concentration these ions cease

8 Journal of Nanoscience

minus70

00

70

minus150

000

150

minus20 0 20

minus20 0 20

300 x = 000

300 x = 010

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

00minus20 0 20

300 x = 005

Voltage (V)Curr

ent (I)

minus10

10

300 x = 015

00

Curr

ent (I)

minus10

10

minus20 0 20

Voltage (V)

times10minus6

times10minus6

times10minus6

times10minus6

(a)

minus20 0 20 minus20 0 20

minus20 0 20 minus20 0 20

500 x = 000500 x = 005

500 x = 010500 x = 015

30

00

10

00

minus10

minus30minus10

minus70

00

1070

00

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus3

times10minus7

times10minus4

times10minus5

(b)

minus20 0 20 minus20 0 20

minus20 0 20minus20 0 20

700 x = 000700 x = 005

700 x = 010700 x = 015

minus50

00

50

minus50

00

50

minus20

00

20

minus60

00

60

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus6

times10minus6

times10minus8

times10minus5

(c)

minus20 0 20 minus20 0 20

minus20 0 20 minus20 0 20

900 x = 005

900 x = 010900 x = 015

900 x = 000

minus10

10

minus10

00

00 00

10

minus50

00

50

minus30

30

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus6 times10

minus7

times10minus5

times10minus7

(d)

Figure 6 119868-119881 curves of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at different temperatures (a) 300∘C (b) 500∘C (c) 700∘C and

(d) 900∘C

to be dissolved resulting in the presence of Dy3+ ions atgrain boundaries at higher dopant concentration On theother hand low sintering leads to incomplete crystallizationhowever crystallization is prominent at higher sintering tem-perature [19] The value of dielectric constant in the presentcase is affected by oxidation state of metallic ions methodof synthesis and also the solubility of Dy3+ ion This aspectwas studied for nickel ferrite system [20] Method of syn-thesis plays an important role in determining the dielectric

properties Synthesis routes which involve comparatively lowheat treatment exhibit higher value of dielectric constantand high value of dielectric loss due to presence of organicfree radicals and metastable phases This type of behaviourwas studied by Singh et al [20] Coprecipitation methodrequires comparatively higher value of thermal treatmentthan the nitrate route This may be one reason for changein the dielectric constant [8] Another issue is the solubilityof rare earth ions in the ferrite matrix The rare earth ions

Journal of Nanoscience 9

with larger ionic radii have limited solubility in the latticeThe trace amount of the phase which could not be detectedby XRD such as the presence of Dy3+ ions on grain bound-aries may take part in polarization processes and may causean increase in the dielectric constant of the materials

35 Dielectric Loss Dielectric tangent loss (tan 120575) ofCoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) was calculated

using the relation [16]

tan 120575 = 1205761015840

12057610158401015840 (2)

where 12057610158401015840 is the imaginary part of the dielectric constant andis a measure of the absorption of energy by the dielectricmaterial from the alternating field 120575 is the loss angle and 1205761015840is the real part of the dielectric constant The dielectric losstangent versus frequency is shown in Figure 5 The valuesof the dielectric tangent loss (tan 120575) at different sinteringtemperature are tabulated in Table 5 The dielectric tangentloss (tan 120575) decreases with increase in the frequency andthen becomes constant at higher frequencies for each sampleThe value of dielectric tangent loss (tan 120575) depends on anumber of factors such as stoichiometry Fe+2 content andstructural homogeneity which in turn depend on the com-position and synthesis methods The decrease in loss tangentwith frequency may be attributed to the Maxwell-Wagnerpolarization [17] and conduction mechanism in ferritesThe dielectric loss tangent (tan 120575) changes with increase inthe dysprosium (Dy3+) concentration in cobalt ferrite Anincrease in the dielectric loss tangent was observed for thecase of undoped cobalt ferrite sintered at 700 and 900∘C

36 I-VCharacteristic Theelectrical resistivity of the sampleswas calculated using the formula

120588 = 119877

119860

119871

(3)

where 119871 is the thickness 119877 is the resistance and 119860 is thearea (119860 = 1205871199032) of the pellet Figures 6(a)ndash6(d) showthe I-V characteristics of the samples sintered at differenttemperatures The value of electrical resistivity at roomtemperature is tabulated in Table 6 The electrical resistivitydepends upon the crystal structure and composition of thematerials It changes with the increase in the dysprosium(Dy3+) concentration In the present case of CoFe

2minus119909Dy119909O4

(119909 = 000 005 010 and 015) samples it varies in therange of 18 times 105 to 162 times 109Ω-cm for different sinteringtemperatures The electrical resistivity of MnndashZnndashCe ferriteshas also been reported in the range of 14 times 105 to 43 times108Ω-cm [21] However other reports show the electricalresistivity in the range 64 times 105 to 3331 times 106Ω-cm [8] Thetemperature variation of resistivity of these materials is inprogress

4 Conclusions

The XRD TEM FTIR dielectric constant dielectric tangentloss and electrical behaviour of CoFe

2minus119909Dy119909O4(119909 = 000

005 010 and 015) was studied In the present case the bandpositions of FTIR appearing at the higher wave number(ie ]

1= 500ndash600 cmminus1) are assigned to the tetrahedral

complexes while lower wave number (]2= 400ndash450 cmminus1)

is assigned to the octahedral complexes This shows theformation of pure spinel structure of dysprosium dopedcobalt ferrite The dielectric constant of the dysprosiumdoped cobalt ferrite (CoFe

2minus119909Dy119909O4) in general decreases

with the increase in the frequency However some deviationwas observed from this usual behaviour For the samplesintered at 300∘C the dielectric constant is almost unchangedwith frequency at the particular concentrations of 119909 = 000and 005 Similar result is obtained for the sample sintered at500∘C (119909 = 010 015) 700∘C (119909 = 005 010 and 015) and900∘C (119909 = 005 010) The values of electrical resistivity ofthe materials are in the range of 105ndash109Ω-cm which may besuitable for the high frequency applicationsThe high value ofdielectric constant is useful in capacitor dielectrics The lowvalue of dielectric constant is used as microwave absorbers inhigh frequency applications In the present study the differentcompositions of the materials are suitable for both low andhigh dielectric constant applications

Conflict of Interests

The authors declare that they have no conflict of interestsregarding the publication of this paper

Acknowledgment

Hemaunt Kumar is thankful to Dr Mukul Gupta (UGCDAECSR Indore Centre) for the keen interest and suggestions inXRD measurements and also thankful to Dr Ranjan KumarSingh (Department of Physics BHU) for providing the FTIRfacilities

References

[1] S Gubbala H Nathani K Koziol and R D K Misra ldquoMag-netic properties of nanocrystalline NindashZn ZnndashMn and NindashMn ferrites synthesized by reverse micelle techniquerdquo PhysicaB Condensed Matter vol 348 no 1ndash4 pp 317ndash328 2004

[2] B Viswanathan and V R K Murthy Ferrite Materials Scienceand Technology Narosa New Delhi India 1990

[3] J-G Lee J Y Park and C S Kim ldquoGrowth of ultra-finecobalt ferrite particles by a solndashgel method and their magneticpropertiesrdquo Journal ofMaterials Science vol 33 no 15 pp 3965ndash3968 1998

[4] S N Okuno S Hanshimoto and K Inomata ldquoPreferredcrystal orientation of cobalt ferrite thin films induced by ionbombardment during deposition rdquo Journal of Applied Physicsvol 71 no 12 pp 5926ndash5929 1992

[5] H R C S Andradea L M Searaa and N D S MohallemaldquoSynthesis and characterization of BaTiO

3CoFe

2O4thin filmsrdquo

MRS Proceedings vol 1368 2011

[6] G Sathishkumar C Venkataraju and K Sivakumar ldquoSynthesisstructural and dielectric studies of nickel substituted cobalt-zinc

10 Journal of Nanoscience

ferriterdquo Materials Sciences and Applications vol 1 pp 19ndash242010

[7] G D Dwivedi K F Tseng C L Chan et al ldquoSignature offerroelectricity in magnetically ordered Mo-doped CoFe

2O4rdquo

Physical Review B CondensedMatter andMaterials Physics vol82 Article ID 134428 2010

[8] P Kumar S K Sharma andM Singh ldquoEffect of La3+ doping onthe electric dielectric and magnetic properties of cobalt ferriteprocessed by co-precipitation techniquerdquo Journal of Alloys andCompounds vol 508 no 1 pp 115ndash118 2010

[9] E Pervaiz and I H Gul ldquoStructural electrical and magneticstudies of Gd3+ doped cobalt ferrite nanoparticlesrdquo Interna-tional Journal of Current Engineering and Technology vol 2 pp377ndash387 2012

[10] M L Kahn and Z J Zhang ldquoSynthesis andmagnetic propertiesof CoFe

2O4spinel ferrite nanoparticles doped with lanthanide

ionsrdquoApplied Physics Letters vol 78 no 23 pp 3651ndash3653 2001[11] XMeng H Li J Chen L Mei KWang and X Li ldquoMossbauer

study of cobalt ferrite nanocrystals substituted with rare-earthY3+ ionsrdquo Journal ofMagnetism andMagneticMaterials vol 321no 9 pp 1155ndash1158 2009

[12] A T Raghavender R G Kulkarni and KM Jadhav ldquoMagneticproperties of mixed cobalt-aluminum ferrite nanoparticlesrdquoChinese Journal of Physics vol 48 no 4 pp 512ndash522 2010

[13] R M Mohamed M M Rashad F A Haraz and W Sig-mund ldquoStructure and magnetic properties of nanocrystallinecobalt ferrite powders synthesized using organic acid precursormethodrdquo Journal ofMagnetism andMagneticMaterials vol 322no 14 pp 2058ndash2064 2010

[14] M Gharagozlou ldquoSynthesis and characterization of nanocrys-talline magnetic pigment via coordinated precursorsrdquo Progressin Color Colorants and Coatings vol 2 no 1 pp 35ndash43 2009

[15] M A Ahmed E Ateia and F M Salem ldquoSpectroscopic andelectrical properties of MgndashTi ferrite doped with different rare-earth elementsrdquo Physica B Condensed Matter vol 381 no 1-2pp 144ndash155 2006

[16] K M Batoo ldquoStructural and electrical properties of Cu dopedNiFe2O4nanoparticles prepared through modified citrate gel

methodrdquo Journal of Physics and Chemistry of Solids vol 72 no12 pp 1400ndash1407 2011

[17] J C Maxwell A Treatise on Electricity and Magnetisim vol 1Oxford University Press New York NY USA 1973

[18] K W Wanger ldquoZur theorie der unvollkommenen dilektrikardquoAnnalen der Physik vol 345 no 5 pp 817ndash855 1913

[19] J P Singh C L Chen C L Dong et al ldquoEffect of intermediateannealing on the structural electrical and dielectric propertiesof zinc ferrite an XANES investigationrdquo Science of AdvancedMaterials vol 5 no 2 pp 171ndash181 2013

[20] J P Singh G Dixit R C Srivastava H M Agrawal andK Asokan ldquoLooking for the possibility of multiferroism inNiGd

004Fe196

O4nanoparticle systemrdquo Journal of Physics D

Applied Physics vol 44 no 43 Article ID 435306 2011[21] D Ravinder and B R Kumar ldquoElectrical conductivity of cerium

substitutedMnndashZn ferritesrdquoMaterials Letters vol 57 no 11 pp1738ndash1742 2003

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

2 Journal of Nanoscience

Table 1 Calculated XRD parameters of the samples CoFe2minus119909

Dy119909O4sintered at 500∘C

Samples Crystallite size(plusmn1 nm)

Lattice parameter(plusmn001 A)

X-ray density(plusmn002 gmcm3)

Specific surface area(plusmn1m2gm)

119909 = 000 22 837 533 51119909 = 005 16 837 544 69119909 = 010 13 836 557 83119909 = 015 11 836 569 96

low values of dielectric constant dielectric loss andmagneticloss could be correlated with better compositional stoichiom-etry and Fe ions concentrationThe structural electrical andmagnetic studies of Gd3+ doped cobalt ferrite nanoparticleswere investigated and these materials show low loss highresistivity and soft magnetic properties due to Gd3+ doping[9]

It was observed that rare earth doped ferrite exhibitsbetter properties however limited solubility of these ions inferrite is a major issue Moreover the solubility limit dependson the method of synthesis [8] In the lanthanide series themagnetic moment varies from 0 (La3+) to 105 120583B (Dy3+) andlanthanide ions can be isotropic or anisotropic due to thelarge variation of the f-electron orbital contribution to themagnetic interaction The magnetic properties of rare earthdoped ferrites are not well understood either in terms of themagnetic moment of the dopant cations or the unpaired f-electrons [10] Among the lanthanide series Dy3+ ion hasthe highest value of magnetic moment which affects themagnetic and electrical properties of the materials Thereare several issues related to the rare earth ions doping inferrites such as limited solubility of rare earth ions and itseffect on the electrical and magnetic properties which arenot well understood Hence the present work is carried outto get an insight of the underlying physics by performingXRD TEM Fourier transform infrared spectroscopy (FTIR)and dielectric and electrical resistivity measurements of Dy3+doped ferrite

2 Experimental

Nanoparticles of dysprosium doped cobalt ferrite weresynthesized by using the chemical route The stoichio-metric amounts of Fe(NO

3)3sdot9H2O Co(NO

3)2sdot6H2O and

Dy(NO3)3sdot5H2O were dissolved in the distilled water In the

aqueous salt solution citric acid solution was added with thecations to citric acid molar ratio of 1 2 The solution washeated at 85∘C under constant magnetic stirring until thesolution got converted into a viscous gel and was allowed tocool at room temperature The cooled gel was dried in anoven at 100∘C for overnight to form the precursor materialThe precursor material was sintered at 300 500 700 and900∘C for 2 hrs to get the nanoparticles of dysprosium dopedcobalt ferrite X-ray diffraction data were collected on BrukerD8 ADVANDEDX-ray diffractometer using Cu K

120572radiation

(120582 = 154178 A) The ferrite powder was pressed into pelletsof 10mm diameter at a presser of 5 ton after mixing withabout 2 by weight of polyvinyl alcohol binderThese pellets

15 30 45 60

Inte

nsity

(au

)

2120579 (deg)

x = 015

x = 010

x = 005

(111) (220)(311)

(222) (400) (422)(511) (440)

x = 000 500∘C

Figure 1 XRD patterns of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp

015) sintered at temperature of 500∘C

were heated in a furnace at 200∘C for 2 hrs These pelletswere polished and coated with silver on both surfaces fordielectric measurements The dielectric properties of thesamples weremeasuredwith anAgilent 4285A precision LCRmeter in the frequency range of 75 kHz to 5MHz Fouriertransform infrared spectroscopy (FTIR) was recorded atroom temperature in the range of 200 to 4000 cmminus1 usingBruker make Vortex 70 spectrometer

3 Results and Discussion

31 XRD Study Figure 1 shows the representative X-raydiffraction patterns of CoFe

2minus119909Dy119909O4(119909 = 000 005 010

and 015) samples sintered at 500∘CThe synthesized samplesexhibit the presence of cubic spinel phase (JCPDS number-03-0864) No impurity phase was detected even for thehighest concentration of Dy3+ (119909 = 015) All the XRD peakscould be indexed to Fd3m space group with cubic symmetryIt is observed that the XRD peaks of the samples appear tobe broadened with increasing Dy3+ concentration The XRDparameters such as crystallite size lattice parameters X-raydensity and specific surface area are tabulated in Table 1The higher concentration of Dy3+ led to lower crystallinityof the all the samples This may be because more dopantconcentration leads to a higher potential barrier thatDy3+ ionhas to overcome for entering the spinel crystal lattice resultingin crystal lattice distortion and local strain [11]

32 TEM Study Few representative transmission electronmicrographs of the dysprosium doped cobalt ferrite nanopar-ticles at the sintering temperature of 700∘C are shownin Figure 2 The average particle sizes are 49 40 43 and37 nm for the concentration of 119909 = 000 005 010 and015 respectively (Table 2) In the present case the particle

Journal of Nanoscience 3

0 20 40 60 80

8

6

4

2

0

Freq

uenc

y co

unt

Particle size (nm)

x = 000

(a)

0 20 40 60 80

18

16

14

12

10

8

6

4

2

0

Freq

uenc

y co

unt

Particle size (nm)

x = 005

(b)

0 20 40 60 80

8

6

4

2

0

Freq

uenc

y co

unt

Particle size (nm)

x = 010

(c)

x = 015

0 20 40 60 80

8

6

4

2

0

Freq

uenc

y co

unt

Particle size (nm)

(d)

Figure 2 TEMmicrographs of CoFe2minus119909

Dy119909O4sintered at 700∘C (a) 119909 = 000 (b) 119909 = 005 (c) 119909 = 010 (d) 119909 = 015

4 Journal of Nanoscience

400 800 1200 1600 2000 2400 2800 3200 3600 4000

3450 cmminus1

3460 cmminus1

2350 cmminus1

2352 cmminus1

2338 cmminus1

3430 cmminus1

3462 cmminus1

2330 cmminus1

1632 cmminus1

1640 cmminus1

1620 cmminus1

1373 cmminus1

1380 cmminus1

1400 cmminus1

1605 cmminus1

Tran

smiss

ion

()

x = 0001393 cmminus1

x = 005

x = 010

1 2

x = 015

300∘C

Wavenumber (cmminus1)

(a)

400 800 1200 1600 2000 2400 2800 3200 3600 4000

Tran

smiss

ion

()

x = 000

x = 005

x = 010

x = 015

500∘C

Wavenumber (cmminus1)

(b)

400 800 1200 1600 2000 2400 2800 3200 3600 4000

Tran

smiss

ion

()

x = 000

x = 005

x = 010

x = 015

700∘C

Wavenumber (cmminus1)

(c)

400 800 1200 1600 2000 2400 2800 3200 3600 4000

Tran

smiss

ion

()

x = 005

x = 010

x = 015

x = 000 900∘C

Wavenumber (cmminus1)

(d)

Figure 3 FTIR spectra of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at different temperatures of (a) 300∘C (b) 500∘C (c) 700∘C

and (d) 900∘C

Table 2 Particle size of samples CoFe2minus119909

Dy119909O4sintered at 700∘C

Samples Particle size (nm)119909 = 000 49119909 = 005 40119909 = 010 43119909 = 015 37

size is more than that of the crystallite size indicating thatthe particles of the synthesized samples consist of severalcrystallites A decreasing trend of particle size was observedwith the increase of Dy3+ concentration Similar behaviour ofparticle size was observed by other workers also [12]

33 FTIR Study FTIR spectra of dysprosium doped cobaltferrite which were synthesized at different sintering tem-peratures (300ndash900∘C) were recorded in the range of 400ndash5000 cmminus1 at room temperature The obtained results areshown in Figures 3(a)ndash3(d) In ferrites the band appearingat the higher wave number (]

1 500ndash600 cmminus1) is assigned

to the tetrahedral complexes while the band appearing atlower wave number (]

2 400ndash450 cmminus1) is assigned to the

octahedral complexesThe higher wave number ]1represents

the vibration of Fe3+ndashO2minus in the sublattice site A while thelower wave number band ]

2represents the trivalent metal-

oxygen vibration at the octahedral B-sites The differencein the ]

1and ]

2band positions is expected because of the

difference in the Fe3+ndashO2minus distance for the octahedral andthe tetrahedral sites [13] It is seen that the FTIR spectra ofthe dysprosium doped cobalt ferrite nanoparticles show noresidual organic compounds and confirm the formation ofthe organic free dysprosium doped cobalt ferrite above thesintering temperature of 500∘C At lower sintering tempera-ture (300∘C) of dysprosiumdoped cobalt ferrite the observedpeak at about 3410 cmminus1 is attributed to the stretchingvibration of the hydroxyl group and the other observed peaksat around 1400 and 1600 cmminus1 are attributed to the symmetricand asymmetric stretching vibration of CO

2groups The

observed peak around 2330ndash2358 cmminus1 is assigned to thealiphatic and aromatic CndashH bond stretching These bandsstart removing for higher sintering temperature due to theevaporation of CO

2[14]The ratio of the line position of FTIR

bands can be determined by [15] ]1]2= (1198701199051198700)radic2 where

119870119905and119870

0are the force constants for theMndashO bonds in tetra-

hedral and octahedral sites respectively Deviation of theratio119870

1199051198700fromunity indicates that the expansion at one site

is not equally compensated by the shrinkage at another siteIn the present case the peak around 800 cmminus1 becomes more

Journal of Nanoscience 5

Table 3 FTIR data of CoFe2minusxDyxO4 samples sintered at 300 500 700 and 900∘C

Samples 300∘C 500∘C 700∘C 900∘C]1(cmminus1) ]

2(cmminus1) ]

1(cmminus1) ]

2(cmminus1) ]

1(cmminus1) ]

2(cmminus1) ]

1(cmminus1) ]

2(cmminus1)

119909 = 000 567 403 553 410 567 410 560 417119909 = 005 574 417 581 411 574 417 581 417119909 = 010 581 424 594 430 584 417 587 424119909 = 015 594 424 595 437 587 424 594 430

Table 4 Dielectric constant of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) at different sintering temperatures

Samples FrequencyDielectric constant (1205761015840) at different sintering temperatures

300∘C 500∘C 700∘C 900∘C

119909 = 000

75 kHz 180 1127 834 3441MHz 177 1370 1017 3855MHz 173 1559 1143 473

119909 = 005

75 kHz 248 391 567 1491MHz 246 273 567 1495MHz 241 242 557 146

119909 = 010

75 kHz 495 293 267 2201MHz 297 282 263 2205MHz 276 274 257 216

119909 = 015

75 kHz 245 160 183 6921MHz 160 151 180 6795MHz 171 146 183 665

and more narrower with increasing sintering temperaturewhich is due to the grain growth of the particles with increasein sintering temperature The band positions of dysprosiumdoped cobalt ferrite sintered at 300∘C are in the range of567 cmminus1 to 594 cmminus1 for ]

1and 403 cmminus1 to 424 cmminus1 for ]

2

The band positions of the samples sintered 500∘C are in therange of 553 cmminus1 to 595 cmminus1 for ]

1and 410 cmminus1 to 437 cmminus1

for ]2 The band positions of the samples sintered 700∘C are

in the range 567 cmminus1 to 587 cmminus1 for ]1and 410 cmminus1 to

424 cmminus1 for ]2 The band positions of the samples sintered

900∘C are in the range of 560 cmminus1 to 594 cmminus1 for ]1and

417 cmminus1 to 430 cmminus1 for ]2 The vibrational band positions

for all the samples are shown in Table 3 It is observed thatsubstitution of Fe3+ by Dy3+ causes shifting of band positions(Fe3+ndashO2minus) towards higher frequency side due to increasedbond length at B-sites and lattice distortionThis also suggeststhe occupancy of Dy3+ at B-sites

34 Dielectric Behaviour The dielectric constant 1205761015840 of dys-prosium doped cobalt (CoFe

2minus119909Dy119909O4) ferrite has been esti-

mated from capacitance 119862 of the pellets using the formulagiven below [16]

1205761015840=

119862119889

1205760119860

(1)

where 119889 is the thickness of the pellets 119860 is the cross-sectional area in m2 and 120576

0is the permittivity of free space

The variation of dielectric constant against frequency fordifferent samples is shown in Figure 4The values of dielectricconstant are shown in Table 4 The dielectric constant of thedysprosium doped cobalt ferrite (CoFe

2minus119909Dy119909O4) in general

decreases with the increase in the frequency However in thepresent case some deviation was observed from this usualbehaviour For the sample sintered at 300∘C the dielectricconstant is almost unchanged with the frequency at theparticular concentrations of 119909 = 000 and 005 Similar resultis obtained for the sample sintered at 500∘C (119909 = 010 015)700∘C (119909 = 005 010 and 015) and 900∘C (119909 = 005 010)An increase in the dielectric constant was observed for theundoped cobalt ferrite sintered at 500 700 and 900∘C Thedecrease of dielectric constant with increasing frequency isdue to the fact that above certain frequency of the electricfield the electron exchange between Fe2+ and Fe3+ ion cannotfollow the variation of electric fieldThe space charge carriersin a dielectric material require a finite time to line up theiraxes parallel to the direction of the applied electric field If thefrequency of the field increases a point is reached when thespace charge carriers cannot cope up with the applied fieldAs a result the dielectric constant of thesematerials decreasesAs the frequency of the field continuously increases at somestage the space charge polarization would barely have started

6 Journal of Nanoscience

0 1 2 3 4

1600

1400

1200

1000

800

600

400

200

5

1100

1000

900

800

700

600

500

400

300

200

700

600

500

400

300

200

500

450

400

350

300

250

200

150

500 x = 000

500 x = 005

500 x = 010

500 x = 015

700 x = 000

700 x = 005

700 x = 010

700 x = 015

900 x = 000

900 x = 005

900 x = 010

900 x = 015

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)

Die

lect

ric co

nsta

nt

Die

lect

ric co

nsta

ntD

iele

ctric

cons

tant

Die

lect

ric co

nsta

nt

300 x = 000

300 x = 005

300 x = 010

300 x = 015

0 1 2 3 4 5

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)times106

times106

times106

times106

Figure 4 Dielectric constant of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at 300 500 700 and 900∘C

Table 5 Dielectric loss tangent (tan 120575) of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) at different sintering temperatures

Samples Frequency Dielectric tangent loss (tan 120575) at different sintering temperatures300∘C 500∘C 700∘C 900∘C

119909 = 000

75 kHz 0037 0045 0034 00281MHz 0005 0158 0151 01595MHz 0001 0072 0067 0118

119909 = 005

75 kHz 0010 179 00005 000021MHz 0001 0253 00002 000015MHz 0001 00136 00001 0001

119909 = 010

75 kHz 2006 0195 0041 000091MHz 0343 0022 000481 000075MHz 0073 0005 0003 00006

119909 = 015

75 kHz 1644 0159 0051 003951MHz 0222 0026 000481 0004565MHz 0142 0001 0003 00107

Journal of Nanoscience 7

700 x = 000

700 x = 005

700 x = 010

700 x = 015

900 x = 000

900 x = 005

900 x = 010

900 x = 015

0 1 2 3 4 5

500 x = 000

500 x = 005

500 x = 010

500 x = 015

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)

300 x = 000

300 x = 005

300 x = 010

300 x = 015

18

15

12

09

06

03

00

018 016

012

008

004

000

015

012

009

006

003

000

20

15

10

05

00

Die

lect

ric lo

ssD

iele

ctric

loss

Die

lect

ric lo

ssD

iele

ctric

loss

0 1 2 3 4 5

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)times106

times106

times106

times106

Figure 5 Dielectric loss in CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at 300 500 700 and 900∘C

Table 6 Electrical resistivity (120588) of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) at different sintering temperatures

Samples Electrical resistivity (Ω-cm) at different sintering temperatures300∘C 500∘C 700∘C 900∘C

119909 = 000 176 times 107

587 times 107

807 times 106

188 times 106

119909 = 005 683 times 107

18 times 105

787 times 108

162 times 109

119909 = 010 626 times 107

631 times 105

495 times 106

116 times 108

119909 = 015 1245 times 107

2568 times 105

2437 times 106

684 times 106

to move before the field reverses and makes virtually nocontribution to the polarization and hence to dielectricThe increase in dielectric constant with frequency may bedue to resonance effect The resonance may arise due tothe matching of the frequency of charge transfer betweenFe2+ harr Fe3+ ions and that of the applied electric fieldSimilar increase in the dielectric constant was obtained forthe La doped cobalt ferrite [8 17 18]The change in dielectricconstant with increasing dysprosium concentration may be

due to the migration of the Fe3+ ions from octahedral site totetrahedral site A similar behaviour was reported in case ofthe nickel substituted CondashZn ferrite [6] It has been reportedthat dielectric properties of materials are sensitive to themethod of synthesis microstructure and crystallite size Inthe present case two factors which have dominant effectare sintering temperature and concentration of dopant ionsAt lower concentration Dy3+ ions are dissolved in spinellattice however at higher concentration these ions cease

8 Journal of Nanoscience

minus70

00

70

minus150

000

150

minus20 0 20

minus20 0 20

300 x = 000

300 x = 010

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

00minus20 0 20

300 x = 005

Voltage (V)Curr

ent (I)

minus10

10

300 x = 015

00

Curr

ent (I)

minus10

10

minus20 0 20

Voltage (V)

times10minus6

times10minus6

times10minus6

times10minus6

(a)

minus20 0 20 minus20 0 20

minus20 0 20 minus20 0 20

500 x = 000500 x = 005

500 x = 010500 x = 015

30

00

10

00

minus10

minus30minus10

minus70

00

1070

00

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus3

times10minus7

times10minus4

times10minus5

(b)

minus20 0 20 minus20 0 20

minus20 0 20minus20 0 20

700 x = 000700 x = 005

700 x = 010700 x = 015

minus50

00

50

minus50

00

50

minus20

00

20

minus60

00

60

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus6

times10minus6

times10minus8

times10minus5

(c)

minus20 0 20 minus20 0 20

minus20 0 20 minus20 0 20

900 x = 005

900 x = 010900 x = 015

900 x = 000

minus10

10

minus10

00

00 00

10

minus50

00

50

minus30

30

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus6 times10

minus7

times10minus5

times10minus7

(d)

Figure 6 119868-119881 curves of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at different temperatures (a) 300∘C (b) 500∘C (c) 700∘C and

(d) 900∘C

to be dissolved resulting in the presence of Dy3+ ions atgrain boundaries at higher dopant concentration On theother hand low sintering leads to incomplete crystallizationhowever crystallization is prominent at higher sintering tem-perature [19] The value of dielectric constant in the presentcase is affected by oxidation state of metallic ions methodof synthesis and also the solubility of Dy3+ ion This aspectwas studied for nickel ferrite system [20] Method of syn-thesis plays an important role in determining the dielectric

properties Synthesis routes which involve comparatively lowheat treatment exhibit higher value of dielectric constantand high value of dielectric loss due to presence of organicfree radicals and metastable phases This type of behaviourwas studied by Singh et al [20] Coprecipitation methodrequires comparatively higher value of thermal treatmentthan the nitrate route This may be one reason for changein the dielectric constant [8] Another issue is the solubilityof rare earth ions in the ferrite matrix The rare earth ions

Journal of Nanoscience 9

with larger ionic radii have limited solubility in the latticeThe trace amount of the phase which could not be detectedby XRD such as the presence of Dy3+ ions on grain bound-aries may take part in polarization processes and may causean increase in the dielectric constant of the materials

35 Dielectric Loss Dielectric tangent loss (tan 120575) ofCoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) was calculated

using the relation [16]

tan 120575 = 1205761015840

12057610158401015840 (2)

where 12057610158401015840 is the imaginary part of the dielectric constant andis a measure of the absorption of energy by the dielectricmaterial from the alternating field 120575 is the loss angle and 1205761015840is the real part of the dielectric constant The dielectric losstangent versus frequency is shown in Figure 5 The valuesof the dielectric tangent loss (tan 120575) at different sinteringtemperature are tabulated in Table 5 The dielectric tangentloss (tan 120575) decreases with increase in the frequency andthen becomes constant at higher frequencies for each sampleThe value of dielectric tangent loss (tan 120575) depends on anumber of factors such as stoichiometry Fe+2 content andstructural homogeneity which in turn depend on the com-position and synthesis methods The decrease in loss tangentwith frequency may be attributed to the Maxwell-Wagnerpolarization [17] and conduction mechanism in ferritesThe dielectric loss tangent (tan 120575) changes with increase inthe dysprosium (Dy3+) concentration in cobalt ferrite Anincrease in the dielectric loss tangent was observed for thecase of undoped cobalt ferrite sintered at 700 and 900∘C

36 I-VCharacteristic Theelectrical resistivity of the sampleswas calculated using the formula

120588 = 119877

119860

119871

(3)

where 119871 is the thickness 119877 is the resistance and 119860 is thearea (119860 = 1205871199032) of the pellet Figures 6(a)ndash6(d) showthe I-V characteristics of the samples sintered at differenttemperatures The value of electrical resistivity at roomtemperature is tabulated in Table 6 The electrical resistivitydepends upon the crystal structure and composition of thematerials It changes with the increase in the dysprosium(Dy3+) concentration In the present case of CoFe

2minus119909Dy119909O4

(119909 = 000 005 010 and 015) samples it varies in therange of 18 times 105 to 162 times 109Ω-cm for different sinteringtemperatures The electrical resistivity of MnndashZnndashCe ferriteshas also been reported in the range of 14 times 105 to 43 times108Ω-cm [21] However other reports show the electricalresistivity in the range 64 times 105 to 3331 times 106Ω-cm [8] Thetemperature variation of resistivity of these materials is inprogress

4 Conclusions

The XRD TEM FTIR dielectric constant dielectric tangentloss and electrical behaviour of CoFe

2minus119909Dy119909O4(119909 = 000

005 010 and 015) was studied In the present case the bandpositions of FTIR appearing at the higher wave number(ie ]

1= 500ndash600 cmminus1) are assigned to the tetrahedral

complexes while lower wave number (]2= 400ndash450 cmminus1)

is assigned to the octahedral complexes This shows theformation of pure spinel structure of dysprosium dopedcobalt ferrite The dielectric constant of the dysprosiumdoped cobalt ferrite (CoFe

2minus119909Dy119909O4) in general decreases

with the increase in the frequency However some deviationwas observed from this usual behaviour For the samplesintered at 300∘C the dielectric constant is almost unchangedwith frequency at the particular concentrations of 119909 = 000and 005 Similar result is obtained for the sample sintered at500∘C (119909 = 010 015) 700∘C (119909 = 005 010 and 015) and900∘C (119909 = 005 010) The values of electrical resistivity ofthe materials are in the range of 105ndash109Ω-cm which may besuitable for the high frequency applicationsThe high value ofdielectric constant is useful in capacitor dielectrics The lowvalue of dielectric constant is used as microwave absorbers inhigh frequency applications In the present study the differentcompositions of the materials are suitable for both low andhigh dielectric constant applications

Conflict of Interests

The authors declare that they have no conflict of interestsregarding the publication of this paper

Acknowledgment

Hemaunt Kumar is thankful to Dr Mukul Gupta (UGCDAECSR Indore Centre) for the keen interest and suggestions inXRD measurements and also thankful to Dr Ranjan KumarSingh (Department of Physics BHU) for providing the FTIRfacilities

References

[1] S Gubbala H Nathani K Koziol and R D K Misra ldquoMag-netic properties of nanocrystalline NindashZn ZnndashMn and NindashMn ferrites synthesized by reverse micelle techniquerdquo PhysicaB Condensed Matter vol 348 no 1ndash4 pp 317ndash328 2004

[2] B Viswanathan and V R K Murthy Ferrite Materials Scienceand Technology Narosa New Delhi India 1990

[3] J-G Lee J Y Park and C S Kim ldquoGrowth of ultra-finecobalt ferrite particles by a solndashgel method and their magneticpropertiesrdquo Journal ofMaterials Science vol 33 no 15 pp 3965ndash3968 1998

[4] S N Okuno S Hanshimoto and K Inomata ldquoPreferredcrystal orientation of cobalt ferrite thin films induced by ionbombardment during deposition rdquo Journal of Applied Physicsvol 71 no 12 pp 5926ndash5929 1992

[5] H R C S Andradea L M Searaa and N D S MohallemaldquoSynthesis and characterization of BaTiO

3CoFe

2O4thin filmsrdquo

MRS Proceedings vol 1368 2011

[6] G Sathishkumar C Venkataraju and K Sivakumar ldquoSynthesisstructural and dielectric studies of nickel substituted cobalt-zinc

10 Journal of Nanoscience

ferriterdquo Materials Sciences and Applications vol 1 pp 19ndash242010

[7] G D Dwivedi K F Tseng C L Chan et al ldquoSignature offerroelectricity in magnetically ordered Mo-doped CoFe

2O4rdquo

Physical Review B CondensedMatter andMaterials Physics vol82 Article ID 134428 2010

[8] P Kumar S K Sharma andM Singh ldquoEffect of La3+ doping onthe electric dielectric and magnetic properties of cobalt ferriteprocessed by co-precipitation techniquerdquo Journal of Alloys andCompounds vol 508 no 1 pp 115ndash118 2010

[9] E Pervaiz and I H Gul ldquoStructural electrical and magneticstudies of Gd3+ doped cobalt ferrite nanoparticlesrdquo Interna-tional Journal of Current Engineering and Technology vol 2 pp377ndash387 2012

[10] M L Kahn and Z J Zhang ldquoSynthesis andmagnetic propertiesof CoFe

2O4spinel ferrite nanoparticles doped with lanthanide

ionsrdquoApplied Physics Letters vol 78 no 23 pp 3651ndash3653 2001[11] XMeng H Li J Chen L Mei KWang and X Li ldquoMossbauer

study of cobalt ferrite nanocrystals substituted with rare-earthY3+ ionsrdquo Journal ofMagnetism andMagneticMaterials vol 321no 9 pp 1155ndash1158 2009

[12] A T Raghavender R G Kulkarni and KM Jadhav ldquoMagneticproperties of mixed cobalt-aluminum ferrite nanoparticlesrdquoChinese Journal of Physics vol 48 no 4 pp 512ndash522 2010

[13] R M Mohamed M M Rashad F A Haraz and W Sig-mund ldquoStructure and magnetic properties of nanocrystallinecobalt ferrite powders synthesized using organic acid precursormethodrdquo Journal ofMagnetism andMagneticMaterials vol 322no 14 pp 2058ndash2064 2010

[14] M Gharagozlou ldquoSynthesis and characterization of nanocrys-talline magnetic pigment via coordinated precursorsrdquo Progressin Color Colorants and Coatings vol 2 no 1 pp 35ndash43 2009

[15] M A Ahmed E Ateia and F M Salem ldquoSpectroscopic andelectrical properties of MgndashTi ferrite doped with different rare-earth elementsrdquo Physica B Condensed Matter vol 381 no 1-2pp 144ndash155 2006

[16] K M Batoo ldquoStructural and electrical properties of Cu dopedNiFe2O4nanoparticles prepared through modified citrate gel

methodrdquo Journal of Physics and Chemistry of Solids vol 72 no12 pp 1400ndash1407 2011

[17] J C Maxwell A Treatise on Electricity and Magnetisim vol 1Oxford University Press New York NY USA 1973

[18] K W Wanger ldquoZur theorie der unvollkommenen dilektrikardquoAnnalen der Physik vol 345 no 5 pp 817ndash855 1913

[19] J P Singh C L Chen C L Dong et al ldquoEffect of intermediateannealing on the structural electrical and dielectric propertiesof zinc ferrite an XANES investigationrdquo Science of AdvancedMaterials vol 5 no 2 pp 171ndash181 2013

[20] J P Singh G Dixit R C Srivastava H M Agrawal andK Asokan ldquoLooking for the possibility of multiferroism inNiGd

004Fe196

O4nanoparticle systemrdquo Journal of Physics D

Applied Physics vol 44 no 43 Article ID 435306 2011[21] D Ravinder and B R Kumar ldquoElectrical conductivity of cerium

substitutedMnndashZn ferritesrdquoMaterials Letters vol 57 no 11 pp1738ndash1742 2003

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Journal of Nanoscience 3

0 20 40 60 80

8

6

4

2

0

Freq

uenc

y co

unt

Particle size (nm)

x = 000

(a)

0 20 40 60 80

18

16

14

12

10

8

6

4

2

0

Freq

uenc

y co

unt

Particle size (nm)

x = 005

(b)

0 20 40 60 80

8

6

4

2

0

Freq

uenc

y co

unt

Particle size (nm)

x = 010

(c)

x = 015

0 20 40 60 80

8

6

4

2

0

Freq

uenc

y co

unt

Particle size (nm)

(d)

Figure 2 TEMmicrographs of CoFe2minus119909

Dy119909O4sintered at 700∘C (a) 119909 = 000 (b) 119909 = 005 (c) 119909 = 010 (d) 119909 = 015

4 Journal of Nanoscience

400 800 1200 1600 2000 2400 2800 3200 3600 4000

3450 cmminus1

3460 cmminus1

2350 cmminus1

2352 cmminus1

2338 cmminus1

3430 cmminus1

3462 cmminus1

2330 cmminus1

1632 cmminus1

1640 cmminus1

1620 cmminus1

1373 cmminus1

1380 cmminus1

1400 cmminus1

1605 cmminus1

Tran

smiss

ion

()

x = 0001393 cmminus1

x = 005

x = 010

1 2

x = 015

300∘C

Wavenumber (cmminus1)

(a)

400 800 1200 1600 2000 2400 2800 3200 3600 4000

Tran

smiss

ion

()

x = 000

x = 005

x = 010

x = 015

500∘C

Wavenumber (cmminus1)

(b)

400 800 1200 1600 2000 2400 2800 3200 3600 4000

Tran

smiss

ion

()

x = 000

x = 005

x = 010

x = 015

700∘C

Wavenumber (cmminus1)

(c)

400 800 1200 1600 2000 2400 2800 3200 3600 4000

Tran

smiss

ion

()

x = 005

x = 010

x = 015

x = 000 900∘C

Wavenumber (cmminus1)

(d)

Figure 3 FTIR spectra of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at different temperatures of (a) 300∘C (b) 500∘C (c) 700∘C

and (d) 900∘C

Table 2 Particle size of samples CoFe2minus119909

Dy119909O4sintered at 700∘C

Samples Particle size (nm)119909 = 000 49119909 = 005 40119909 = 010 43119909 = 015 37

size is more than that of the crystallite size indicating thatthe particles of the synthesized samples consist of severalcrystallites A decreasing trend of particle size was observedwith the increase of Dy3+ concentration Similar behaviour ofparticle size was observed by other workers also [12]

33 FTIR Study FTIR spectra of dysprosium doped cobaltferrite which were synthesized at different sintering tem-peratures (300ndash900∘C) were recorded in the range of 400ndash5000 cmminus1 at room temperature The obtained results areshown in Figures 3(a)ndash3(d) In ferrites the band appearingat the higher wave number (]

1 500ndash600 cmminus1) is assigned

to the tetrahedral complexes while the band appearing atlower wave number (]

2 400ndash450 cmminus1) is assigned to the

octahedral complexesThe higher wave number ]1represents

the vibration of Fe3+ndashO2minus in the sublattice site A while thelower wave number band ]

2represents the trivalent metal-

oxygen vibration at the octahedral B-sites The differencein the ]

1and ]

2band positions is expected because of the

difference in the Fe3+ndashO2minus distance for the octahedral andthe tetrahedral sites [13] It is seen that the FTIR spectra ofthe dysprosium doped cobalt ferrite nanoparticles show noresidual organic compounds and confirm the formation ofthe organic free dysprosium doped cobalt ferrite above thesintering temperature of 500∘C At lower sintering tempera-ture (300∘C) of dysprosiumdoped cobalt ferrite the observedpeak at about 3410 cmminus1 is attributed to the stretchingvibration of the hydroxyl group and the other observed peaksat around 1400 and 1600 cmminus1 are attributed to the symmetricand asymmetric stretching vibration of CO

2groups The

observed peak around 2330ndash2358 cmminus1 is assigned to thealiphatic and aromatic CndashH bond stretching These bandsstart removing for higher sintering temperature due to theevaporation of CO

2[14]The ratio of the line position of FTIR

bands can be determined by [15] ]1]2= (1198701199051198700)radic2 where

119870119905and119870

0are the force constants for theMndashO bonds in tetra-

hedral and octahedral sites respectively Deviation of theratio119870

1199051198700fromunity indicates that the expansion at one site

is not equally compensated by the shrinkage at another siteIn the present case the peak around 800 cmminus1 becomes more

Journal of Nanoscience 5

Table 3 FTIR data of CoFe2minusxDyxO4 samples sintered at 300 500 700 and 900∘C

Samples 300∘C 500∘C 700∘C 900∘C]1(cmminus1) ]

2(cmminus1) ]

1(cmminus1) ]

2(cmminus1) ]

1(cmminus1) ]

2(cmminus1) ]

1(cmminus1) ]

2(cmminus1)

119909 = 000 567 403 553 410 567 410 560 417119909 = 005 574 417 581 411 574 417 581 417119909 = 010 581 424 594 430 584 417 587 424119909 = 015 594 424 595 437 587 424 594 430

Table 4 Dielectric constant of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) at different sintering temperatures

Samples FrequencyDielectric constant (1205761015840) at different sintering temperatures

300∘C 500∘C 700∘C 900∘C

119909 = 000

75 kHz 180 1127 834 3441MHz 177 1370 1017 3855MHz 173 1559 1143 473

119909 = 005

75 kHz 248 391 567 1491MHz 246 273 567 1495MHz 241 242 557 146

119909 = 010

75 kHz 495 293 267 2201MHz 297 282 263 2205MHz 276 274 257 216

119909 = 015

75 kHz 245 160 183 6921MHz 160 151 180 6795MHz 171 146 183 665

and more narrower with increasing sintering temperaturewhich is due to the grain growth of the particles with increasein sintering temperature The band positions of dysprosiumdoped cobalt ferrite sintered at 300∘C are in the range of567 cmminus1 to 594 cmminus1 for ]

1and 403 cmminus1 to 424 cmminus1 for ]

2

The band positions of the samples sintered 500∘C are in therange of 553 cmminus1 to 595 cmminus1 for ]

1and 410 cmminus1 to 437 cmminus1

for ]2 The band positions of the samples sintered 700∘C are

in the range 567 cmminus1 to 587 cmminus1 for ]1and 410 cmminus1 to

424 cmminus1 for ]2 The band positions of the samples sintered

900∘C are in the range of 560 cmminus1 to 594 cmminus1 for ]1and

417 cmminus1 to 430 cmminus1 for ]2 The vibrational band positions

for all the samples are shown in Table 3 It is observed thatsubstitution of Fe3+ by Dy3+ causes shifting of band positions(Fe3+ndashO2minus) towards higher frequency side due to increasedbond length at B-sites and lattice distortionThis also suggeststhe occupancy of Dy3+ at B-sites

34 Dielectric Behaviour The dielectric constant 1205761015840 of dys-prosium doped cobalt (CoFe

2minus119909Dy119909O4) ferrite has been esti-

mated from capacitance 119862 of the pellets using the formulagiven below [16]

1205761015840=

119862119889

1205760119860

(1)

where 119889 is the thickness of the pellets 119860 is the cross-sectional area in m2 and 120576

0is the permittivity of free space

The variation of dielectric constant against frequency fordifferent samples is shown in Figure 4The values of dielectricconstant are shown in Table 4 The dielectric constant of thedysprosium doped cobalt ferrite (CoFe

2minus119909Dy119909O4) in general

decreases with the increase in the frequency However in thepresent case some deviation was observed from this usualbehaviour For the sample sintered at 300∘C the dielectricconstant is almost unchanged with the frequency at theparticular concentrations of 119909 = 000 and 005 Similar resultis obtained for the sample sintered at 500∘C (119909 = 010 015)700∘C (119909 = 005 010 and 015) and 900∘C (119909 = 005 010)An increase in the dielectric constant was observed for theundoped cobalt ferrite sintered at 500 700 and 900∘C Thedecrease of dielectric constant with increasing frequency isdue to the fact that above certain frequency of the electricfield the electron exchange between Fe2+ and Fe3+ ion cannotfollow the variation of electric fieldThe space charge carriersin a dielectric material require a finite time to line up theiraxes parallel to the direction of the applied electric field If thefrequency of the field increases a point is reached when thespace charge carriers cannot cope up with the applied fieldAs a result the dielectric constant of thesematerials decreasesAs the frequency of the field continuously increases at somestage the space charge polarization would barely have started

6 Journal of Nanoscience

0 1 2 3 4

1600

1400

1200

1000

800

600

400

200

5

1100

1000

900

800

700

600

500

400

300

200

700

600

500

400

300

200

500

450

400

350

300

250

200

150

500 x = 000

500 x = 005

500 x = 010

500 x = 015

700 x = 000

700 x = 005

700 x = 010

700 x = 015

900 x = 000

900 x = 005

900 x = 010

900 x = 015

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)

Die

lect

ric co

nsta

nt

Die

lect

ric co

nsta

ntD

iele

ctric

cons

tant

Die

lect

ric co

nsta

nt

300 x = 000

300 x = 005

300 x = 010

300 x = 015

0 1 2 3 4 5

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)times106

times106

times106

times106

Figure 4 Dielectric constant of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at 300 500 700 and 900∘C

Table 5 Dielectric loss tangent (tan 120575) of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) at different sintering temperatures

Samples Frequency Dielectric tangent loss (tan 120575) at different sintering temperatures300∘C 500∘C 700∘C 900∘C

119909 = 000

75 kHz 0037 0045 0034 00281MHz 0005 0158 0151 01595MHz 0001 0072 0067 0118

119909 = 005

75 kHz 0010 179 00005 000021MHz 0001 0253 00002 000015MHz 0001 00136 00001 0001

119909 = 010

75 kHz 2006 0195 0041 000091MHz 0343 0022 000481 000075MHz 0073 0005 0003 00006

119909 = 015

75 kHz 1644 0159 0051 003951MHz 0222 0026 000481 0004565MHz 0142 0001 0003 00107

Journal of Nanoscience 7

700 x = 000

700 x = 005

700 x = 010

700 x = 015

900 x = 000

900 x = 005

900 x = 010

900 x = 015

0 1 2 3 4 5

500 x = 000

500 x = 005

500 x = 010

500 x = 015

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)

300 x = 000

300 x = 005

300 x = 010

300 x = 015

18

15

12

09

06

03

00

018 016

012

008

004

000

015

012

009

006

003

000

20

15

10

05

00

Die

lect

ric lo

ssD

iele

ctric

loss

Die

lect

ric lo

ssD

iele

ctric

loss

0 1 2 3 4 5

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)times106

times106

times106

times106

Figure 5 Dielectric loss in CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at 300 500 700 and 900∘C

Table 6 Electrical resistivity (120588) of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) at different sintering temperatures

Samples Electrical resistivity (Ω-cm) at different sintering temperatures300∘C 500∘C 700∘C 900∘C

119909 = 000 176 times 107

587 times 107

807 times 106

188 times 106

119909 = 005 683 times 107

18 times 105

787 times 108

162 times 109

119909 = 010 626 times 107

631 times 105

495 times 106

116 times 108

119909 = 015 1245 times 107

2568 times 105

2437 times 106

684 times 106

to move before the field reverses and makes virtually nocontribution to the polarization and hence to dielectricThe increase in dielectric constant with frequency may bedue to resonance effect The resonance may arise due tothe matching of the frequency of charge transfer betweenFe2+ harr Fe3+ ions and that of the applied electric fieldSimilar increase in the dielectric constant was obtained forthe La doped cobalt ferrite [8 17 18]The change in dielectricconstant with increasing dysprosium concentration may be

due to the migration of the Fe3+ ions from octahedral site totetrahedral site A similar behaviour was reported in case ofthe nickel substituted CondashZn ferrite [6] It has been reportedthat dielectric properties of materials are sensitive to themethod of synthesis microstructure and crystallite size Inthe present case two factors which have dominant effectare sintering temperature and concentration of dopant ionsAt lower concentration Dy3+ ions are dissolved in spinellattice however at higher concentration these ions cease

8 Journal of Nanoscience

minus70

00

70

minus150

000

150

minus20 0 20

minus20 0 20

300 x = 000

300 x = 010

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

00minus20 0 20

300 x = 005

Voltage (V)Curr

ent (I)

minus10

10

300 x = 015

00

Curr

ent (I)

minus10

10

minus20 0 20

Voltage (V)

times10minus6

times10minus6

times10minus6

times10minus6

(a)

minus20 0 20 minus20 0 20

minus20 0 20 minus20 0 20

500 x = 000500 x = 005

500 x = 010500 x = 015

30

00

10

00

minus10

minus30minus10

minus70

00

1070

00

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus3

times10minus7

times10minus4

times10minus5

(b)

minus20 0 20 minus20 0 20

minus20 0 20minus20 0 20

700 x = 000700 x = 005

700 x = 010700 x = 015

minus50

00

50

minus50

00

50

minus20

00

20

minus60

00

60

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus6

times10minus6

times10minus8

times10minus5

(c)

minus20 0 20 minus20 0 20

minus20 0 20 minus20 0 20

900 x = 005

900 x = 010900 x = 015

900 x = 000

minus10

10

minus10

00

00 00

10

minus50

00

50

minus30

30

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus6 times10

minus7

times10minus5

times10minus7

(d)

Figure 6 119868-119881 curves of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at different temperatures (a) 300∘C (b) 500∘C (c) 700∘C and

(d) 900∘C

to be dissolved resulting in the presence of Dy3+ ions atgrain boundaries at higher dopant concentration On theother hand low sintering leads to incomplete crystallizationhowever crystallization is prominent at higher sintering tem-perature [19] The value of dielectric constant in the presentcase is affected by oxidation state of metallic ions methodof synthesis and also the solubility of Dy3+ ion This aspectwas studied for nickel ferrite system [20] Method of syn-thesis plays an important role in determining the dielectric

properties Synthesis routes which involve comparatively lowheat treatment exhibit higher value of dielectric constantand high value of dielectric loss due to presence of organicfree radicals and metastable phases This type of behaviourwas studied by Singh et al [20] Coprecipitation methodrequires comparatively higher value of thermal treatmentthan the nitrate route This may be one reason for changein the dielectric constant [8] Another issue is the solubilityof rare earth ions in the ferrite matrix The rare earth ions

Journal of Nanoscience 9

with larger ionic radii have limited solubility in the latticeThe trace amount of the phase which could not be detectedby XRD such as the presence of Dy3+ ions on grain bound-aries may take part in polarization processes and may causean increase in the dielectric constant of the materials

35 Dielectric Loss Dielectric tangent loss (tan 120575) ofCoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) was calculated

using the relation [16]

tan 120575 = 1205761015840

12057610158401015840 (2)

where 12057610158401015840 is the imaginary part of the dielectric constant andis a measure of the absorption of energy by the dielectricmaterial from the alternating field 120575 is the loss angle and 1205761015840is the real part of the dielectric constant The dielectric losstangent versus frequency is shown in Figure 5 The valuesof the dielectric tangent loss (tan 120575) at different sinteringtemperature are tabulated in Table 5 The dielectric tangentloss (tan 120575) decreases with increase in the frequency andthen becomes constant at higher frequencies for each sampleThe value of dielectric tangent loss (tan 120575) depends on anumber of factors such as stoichiometry Fe+2 content andstructural homogeneity which in turn depend on the com-position and synthesis methods The decrease in loss tangentwith frequency may be attributed to the Maxwell-Wagnerpolarization [17] and conduction mechanism in ferritesThe dielectric loss tangent (tan 120575) changes with increase inthe dysprosium (Dy3+) concentration in cobalt ferrite Anincrease in the dielectric loss tangent was observed for thecase of undoped cobalt ferrite sintered at 700 and 900∘C

36 I-VCharacteristic Theelectrical resistivity of the sampleswas calculated using the formula

120588 = 119877

119860

119871

(3)

where 119871 is the thickness 119877 is the resistance and 119860 is thearea (119860 = 1205871199032) of the pellet Figures 6(a)ndash6(d) showthe I-V characteristics of the samples sintered at differenttemperatures The value of electrical resistivity at roomtemperature is tabulated in Table 6 The electrical resistivitydepends upon the crystal structure and composition of thematerials It changes with the increase in the dysprosium(Dy3+) concentration In the present case of CoFe

2minus119909Dy119909O4

(119909 = 000 005 010 and 015) samples it varies in therange of 18 times 105 to 162 times 109Ω-cm for different sinteringtemperatures The electrical resistivity of MnndashZnndashCe ferriteshas also been reported in the range of 14 times 105 to 43 times108Ω-cm [21] However other reports show the electricalresistivity in the range 64 times 105 to 3331 times 106Ω-cm [8] Thetemperature variation of resistivity of these materials is inprogress

4 Conclusions

The XRD TEM FTIR dielectric constant dielectric tangentloss and electrical behaviour of CoFe

2minus119909Dy119909O4(119909 = 000

005 010 and 015) was studied In the present case the bandpositions of FTIR appearing at the higher wave number(ie ]

1= 500ndash600 cmminus1) are assigned to the tetrahedral

complexes while lower wave number (]2= 400ndash450 cmminus1)

is assigned to the octahedral complexes This shows theformation of pure spinel structure of dysprosium dopedcobalt ferrite The dielectric constant of the dysprosiumdoped cobalt ferrite (CoFe

2minus119909Dy119909O4) in general decreases

with the increase in the frequency However some deviationwas observed from this usual behaviour For the samplesintered at 300∘C the dielectric constant is almost unchangedwith frequency at the particular concentrations of 119909 = 000and 005 Similar result is obtained for the sample sintered at500∘C (119909 = 010 015) 700∘C (119909 = 005 010 and 015) and900∘C (119909 = 005 010) The values of electrical resistivity ofthe materials are in the range of 105ndash109Ω-cm which may besuitable for the high frequency applicationsThe high value ofdielectric constant is useful in capacitor dielectrics The lowvalue of dielectric constant is used as microwave absorbers inhigh frequency applications In the present study the differentcompositions of the materials are suitable for both low andhigh dielectric constant applications

Conflict of Interests

The authors declare that they have no conflict of interestsregarding the publication of this paper

Acknowledgment

Hemaunt Kumar is thankful to Dr Mukul Gupta (UGCDAECSR Indore Centre) for the keen interest and suggestions inXRD measurements and also thankful to Dr Ranjan KumarSingh (Department of Physics BHU) for providing the FTIRfacilities

References

[1] S Gubbala H Nathani K Koziol and R D K Misra ldquoMag-netic properties of nanocrystalline NindashZn ZnndashMn and NindashMn ferrites synthesized by reverse micelle techniquerdquo PhysicaB Condensed Matter vol 348 no 1ndash4 pp 317ndash328 2004

[2] B Viswanathan and V R K Murthy Ferrite Materials Scienceand Technology Narosa New Delhi India 1990

[3] J-G Lee J Y Park and C S Kim ldquoGrowth of ultra-finecobalt ferrite particles by a solndashgel method and their magneticpropertiesrdquo Journal ofMaterials Science vol 33 no 15 pp 3965ndash3968 1998

[4] S N Okuno S Hanshimoto and K Inomata ldquoPreferredcrystal orientation of cobalt ferrite thin films induced by ionbombardment during deposition rdquo Journal of Applied Physicsvol 71 no 12 pp 5926ndash5929 1992

[5] H R C S Andradea L M Searaa and N D S MohallemaldquoSynthesis and characterization of BaTiO

3CoFe

2O4thin filmsrdquo

MRS Proceedings vol 1368 2011

[6] G Sathishkumar C Venkataraju and K Sivakumar ldquoSynthesisstructural and dielectric studies of nickel substituted cobalt-zinc

10 Journal of Nanoscience

ferriterdquo Materials Sciences and Applications vol 1 pp 19ndash242010

[7] G D Dwivedi K F Tseng C L Chan et al ldquoSignature offerroelectricity in magnetically ordered Mo-doped CoFe

2O4rdquo

Physical Review B CondensedMatter andMaterials Physics vol82 Article ID 134428 2010

[8] P Kumar S K Sharma andM Singh ldquoEffect of La3+ doping onthe electric dielectric and magnetic properties of cobalt ferriteprocessed by co-precipitation techniquerdquo Journal of Alloys andCompounds vol 508 no 1 pp 115ndash118 2010

[9] E Pervaiz and I H Gul ldquoStructural electrical and magneticstudies of Gd3+ doped cobalt ferrite nanoparticlesrdquo Interna-tional Journal of Current Engineering and Technology vol 2 pp377ndash387 2012

[10] M L Kahn and Z J Zhang ldquoSynthesis andmagnetic propertiesof CoFe

2O4spinel ferrite nanoparticles doped with lanthanide

ionsrdquoApplied Physics Letters vol 78 no 23 pp 3651ndash3653 2001[11] XMeng H Li J Chen L Mei KWang and X Li ldquoMossbauer

study of cobalt ferrite nanocrystals substituted with rare-earthY3+ ionsrdquo Journal ofMagnetism andMagneticMaterials vol 321no 9 pp 1155ndash1158 2009

[12] A T Raghavender R G Kulkarni and KM Jadhav ldquoMagneticproperties of mixed cobalt-aluminum ferrite nanoparticlesrdquoChinese Journal of Physics vol 48 no 4 pp 512ndash522 2010

[13] R M Mohamed M M Rashad F A Haraz and W Sig-mund ldquoStructure and magnetic properties of nanocrystallinecobalt ferrite powders synthesized using organic acid precursormethodrdquo Journal ofMagnetism andMagneticMaterials vol 322no 14 pp 2058ndash2064 2010

[14] M Gharagozlou ldquoSynthesis and characterization of nanocrys-talline magnetic pigment via coordinated precursorsrdquo Progressin Color Colorants and Coatings vol 2 no 1 pp 35ndash43 2009

[15] M A Ahmed E Ateia and F M Salem ldquoSpectroscopic andelectrical properties of MgndashTi ferrite doped with different rare-earth elementsrdquo Physica B Condensed Matter vol 381 no 1-2pp 144ndash155 2006

[16] K M Batoo ldquoStructural and electrical properties of Cu dopedNiFe2O4nanoparticles prepared through modified citrate gel

methodrdquo Journal of Physics and Chemistry of Solids vol 72 no12 pp 1400ndash1407 2011

[17] J C Maxwell A Treatise on Electricity and Magnetisim vol 1Oxford University Press New York NY USA 1973

[18] K W Wanger ldquoZur theorie der unvollkommenen dilektrikardquoAnnalen der Physik vol 345 no 5 pp 817ndash855 1913

[19] J P Singh C L Chen C L Dong et al ldquoEffect of intermediateannealing on the structural electrical and dielectric propertiesof zinc ferrite an XANES investigationrdquo Science of AdvancedMaterials vol 5 no 2 pp 171ndash181 2013

[20] J P Singh G Dixit R C Srivastava H M Agrawal andK Asokan ldquoLooking for the possibility of multiferroism inNiGd

004Fe196

O4nanoparticle systemrdquo Journal of Physics D

Applied Physics vol 44 no 43 Article ID 435306 2011[21] D Ravinder and B R Kumar ldquoElectrical conductivity of cerium

substitutedMnndashZn ferritesrdquoMaterials Letters vol 57 no 11 pp1738ndash1742 2003

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

4 Journal of Nanoscience

400 800 1200 1600 2000 2400 2800 3200 3600 4000

3450 cmminus1

3460 cmminus1

2350 cmminus1

2352 cmminus1

2338 cmminus1

3430 cmminus1

3462 cmminus1

2330 cmminus1

1632 cmminus1

1640 cmminus1

1620 cmminus1

1373 cmminus1

1380 cmminus1

1400 cmminus1

1605 cmminus1

Tran

smiss

ion

()

x = 0001393 cmminus1

x = 005

x = 010

1 2

x = 015

300∘C

Wavenumber (cmminus1)

(a)

400 800 1200 1600 2000 2400 2800 3200 3600 4000

Tran

smiss

ion

()

x = 000

x = 005

x = 010

x = 015

500∘C

Wavenumber (cmminus1)

(b)

400 800 1200 1600 2000 2400 2800 3200 3600 4000

Tran

smiss

ion

()

x = 000

x = 005

x = 010

x = 015

700∘C

Wavenumber (cmminus1)

(c)

400 800 1200 1600 2000 2400 2800 3200 3600 4000

Tran

smiss

ion

()

x = 005

x = 010

x = 015

x = 000 900∘C

Wavenumber (cmminus1)

(d)

Figure 3 FTIR spectra of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at different temperatures of (a) 300∘C (b) 500∘C (c) 700∘C

and (d) 900∘C

Table 2 Particle size of samples CoFe2minus119909

Dy119909O4sintered at 700∘C

Samples Particle size (nm)119909 = 000 49119909 = 005 40119909 = 010 43119909 = 015 37

size is more than that of the crystallite size indicating thatthe particles of the synthesized samples consist of severalcrystallites A decreasing trend of particle size was observedwith the increase of Dy3+ concentration Similar behaviour ofparticle size was observed by other workers also [12]

33 FTIR Study FTIR spectra of dysprosium doped cobaltferrite which were synthesized at different sintering tem-peratures (300ndash900∘C) were recorded in the range of 400ndash5000 cmminus1 at room temperature The obtained results areshown in Figures 3(a)ndash3(d) In ferrites the band appearingat the higher wave number (]

1 500ndash600 cmminus1) is assigned

to the tetrahedral complexes while the band appearing atlower wave number (]

2 400ndash450 cmminus1) is assigned to the

octahedral complexesThe higher wave number ]1represents

the vibration of Fe3+ndashO2minus in the sublattice site A while thelower wave number band ]

2represents the trivalent metal-

oxygen vibration at the octahedral B-sites The differencein the ]

1and ]

2band positions is expected because of the

difference in the Fe3+ndashO2minus distance for the octahedral andthe tetrahedral sites [13] It is seen that the FTIR spectra ofthe dysprosium doped cobalt ferrite nanoparticles show noresidual organic compounds and confirm the formation ofthe organic free dysprosium doped cobalt ferrite above thesintering temperature of 500∘C At lower sintering tempera-ture (300∘C) of dysprosiumdoped cobalt ferrite the observedpeak at about 3410 cmminus1 is attributed to the stretchingvibration of the hydroxyl group and the other observed peaksat around 1400 and 1600 cmminus1 are attributed to the symmetricand asymmetric stretching vibration of CO

2groups The

observed peak around 2330ndash2358 cmminus1 is assigned to thealiphatic and aromatic CndashH bond stretching These bandsstart removing for higher sintering temperature due to theevaporation of CO

2[14]The ratio of the line position of FTIR

bands can be determined by [15] ]1]2= (1198701199051198700)radic2 where

119870119905and119870

0are the force constants for theMndashO bonds in tetra-

hedral and octahedral sites respectively Deviation of theratio119870

1199051198700fromunity indicates that the expansion at one site

is not equally compensated by the shrinkage at another siteIn the present case the peak around 800 cmminus1 becomes more

Journal of Nanoscience 5

Table 3 FTIR data of CoFe2minusxDyxO4 samples sintered at 300 500 700 and 900∘C

Samples 300∘C 500∘C 700∘C 900∘C]1(cmminus1) ]

2(cmminus1) ]

1(cmminus1) ]

2(cmminus1) ]

1(cmminus1) ]

2(cmminus1) ]

1(cmminus1) ]

2(cmminus1)

119909 = 000 567 403 553 410 567 410 560 417119909 = 005 574 417 581 411 574 417 581 417119909 = 010 581 424 594 430 584 417 587 424119909 = 015 594 424 595 437 587 424 594 430

Table 4 Dielectric constant of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) at different sintering temperatures

Samples FrequencyDielectric constant (1205761015840) at different sintering temperatures

300∘C 500∘C 700∘C 900∘C

119909 = 000

75 kHz 180 1127 834 3441MHz 177 1370 1017 3855MHz 173 1559 1143 473

119909 = 005

75 kHz 248 391 567 1491MHz 246 273 567 1495MHz 241 242 557 146

119909 = 010

75 kHz 495 293 267 2201MHz 297 282 263 2205MHz 276 274 257 216

119909 = 015

75 kHz 245 160 183 6921MHz 160 151 180 6795MHz 171 146 183 665

and more narrower with increasing sintering temperaturewhich is due to the grain growth of the particles with increasein sintering temperature The band positions of dysprosiumdoped cobalt ferrite sintered at 300∘C are in the range of567 cmminus1 to 594 cmminus1 for ]

1and 403 cmminus1 to 424 cmminus1 for ]

2

The band positions of the samples sintered 500∘C are in therange of 553 cmminus1 to 595 cmminus1 for ]

1and 410 cmminus1 to 437 cmminus1

for ]2 The band positions of the samples sintered 700∘C are

in the range 567 cmminus1 to 587 cmminus1 for ]1and 410 cmminus1 to

424 cmminus1 for ]2 The band positions of the samples sintered

900∘C are in the range of 560 cmminus1 to 594 cmminus1 for ]1and

417 cmminus1 to 430 cmminus1 for ]2 The vibrational band positions

for all the samples are shown in Table 3 It is observed thatsubstitution of Fe3+ by Dy3+ causes shifting of band positions(Fe3+ndashO2minus) towards higher frequency side due to increasedbond length at B-sites and lattice distortionThis also suggeststhe occupancy of Dy3+ at B-sites

34 Dielectric Behaviour The dielectric constant 1205761015840 of dys-prosium doped cobalt (CoFe

2minus119909Dy119909O4) ferrite has been esti-

mated from capacitance 119862 of the pellets using the formulagiven below [16]

1205761015840=

119862119889

1205760119860

(1)

where 119889 is the thickness of the pellets 119860 is the cross-sectional area in m2 and 120576

0is the permittivity of free space

The variation of dielectric constant against frequency fordifferent samples is shown in Figure 4The values of dielectricconstant are shown in Table 4 The dielectric constant of thedysprosium doped cobalt ferrite (CoFe

2minus119909Dy119909O4) in general

decreases with the increase in the frequency However in thepresent case some deviation was observed from this usualbehaviour For the sample sintered at 300∘C the dielectricconstant is almost unchanged with the frequency at theparticular concentrations of 119909 = 000 and 005 Similar resultis obtained for the sample sintered at 500∘C (119909 = 010 015)700∘C (119909 = 005 010 and 015) and 900∘C (119909 = 005 010)An increase in the dielectric constant was observed for theundoped cobalt ferrite sintered at 500 700 and 900∘C Thedecrease of dielectric constant with increasing frequency isdue to the fact that above certain frequency of the electricfield the electron exchange between Fe2+ and Fe3+ ion cannotfollow the variation of electric fieldThe space charge carriersin a dielectric material require a finite time to line up theiraxes parallel to the direction of the applied electric field If thefrequency of the field increases a point is reached when thespace charge carriers cannot cope up with the applied fieldAs a result the dielectric constant of thesematerials decreasesAs the frequency of the field continuously increases at somestage the space charge polarization would barely have started

6 Journal of Nanoscience

0 1 2 3 4

1600

1400

1200

1000

800

600

400

200

5

1100

1000

900

800

700

600

500

400

300

200

700

600

500

400

300

200

500

450

400

350

300

250

200

150

500 x = 000

500 x = 005

500 x = 010

500 x = 015

700 x = 000

700 x = 005

700 x = 010

700 x = 015

900 x = 000

900 x = 005

900 x = 010

900 x = 015

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)

Die

lect

ric co

nsta

nt

Die

lect

ric co

nsta

ntD

iele

ctric

cons

tant

Die

lect

ric co

nsta

nt

300 x = 000

300 x = 005

300 x = 010

300 x = 015

0 1 2 3 4 5

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)times106

times106

times106

times106

Figure 4 Dielectric constant of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at 300 500 700 and 900∘C

Table 5 Dielectric loss tangent (tan 120575) of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) at different sintering temperatures

Samples Frequency Dielectric tangent loss (tan 120575) at different sintering temperatures300∘C 500∘C 700∘C 900∘C

119909 = 000

75 kHz 0037 0045 0034 00281MHz 0005 0158 0151 01595MHz 0001 0072 0067 0118

119909 = 005

75 kHz 0010 179 00005 000021MHz 0001 0253 00002 000015MHz 0001 00136 00001 0001

119909 = 010

75 kHz 2006 0195 0041 000091MHz 0343 0022 000481 000075MHz 0073 0005 0003 00006

119909 = 015

75 kHz 1644 0159 0051 003951MHz 0222 0026 000481 0004565MHz 0142 0001 0003 00107

Journal of Nanoscience 7

700 x = 000

700 x = 005

700 x = 010

700 x = 015

900 x = 000

900 x = 005

900 x = 010

900 x = 015

0 1 2 3 4 5

500 x = 000

500 x = 005

500 x = 010

500 x = 015

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)

300 x = 000

300 x = 005

300 x = 010

300 x = 015

18

15

12

09

06

03

00

018 016

012

008

004

000

015

012

009

006

003

000

20

15

10

05

00

Die

lect

ric lo

ssD

iele

ctric

loss

Die

lect

ric lo

ssD

iele

ctric

loss

0 1 2 3 4 5

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)times106

times106

times106

times106

Figure 5 Dielectric loss in CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at 300 500 700 and 900∘C

Table 6 Electrical resistivity (120588) of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) at different sintering temperatures

Samples Electrical resistivity (Ω-cm) at different sintering temperatures300∘C 500∘C 700∘C 900∘C

119909 = 000 176 times 107

587 times 107

807 times 106

188 times 106

119909 = 005 683 times 107

18 times 105

787 times 108

162 times 109

119909 = 010 626 times 107

631 times 105

495 times 106

116 times 108

119909 = 015 1245 times 107

2568 times 105

2437 times 106

684 times 106

to move before the field reverses and makes virtually nocontribution to the polarization and hence to dielectricThe increase in dielectric constant with frequency may bedue to resonance effect The resonance may arise due tothe matching of the frequency of charge transfer betweenFe2+ harr Fe3+ ions and that of the applied electric fieldSimilar increase in the dielectric constant was obtained forthe La doped cobalt ferrite [8 17 18]The change in dielectricconstant with increasing dysprosium concentration may be

due to the migration of the Fe3+ ions from octahedral site totetrahedral site A similar behaviour was reported in case ofthe nickel substituted CondashZn ferrite [6] It has been reportedthat dielectric properties of materials are sensitive to themethod of synthesis microstructure and crystallite size Inthe present case two factors which have dominant effectare sintering temperature and concentration of dopant ionsAt lower concentration Dy3+ ions are dissolved in spinellattice however at higher concentration these ions cease

8 Journal of Nanoscience

minus70

00

70

minus150

000

150

minus20 0 20

minus20 0 20

300 x = 000

300 x = 010

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

00minus20 0 20

300 x = 005

Voltage (V)Curr

ent (I)

minus10

10

300 x = 015

00

Curr

ent (I)

minus10

10

minus20 0 20

Voltage (V)

times10minus6

times10minus6

times10minus6

times10minus6

(a)

minus20 0 20 minus20 0 20

minus20 0 20 minus20 0 20

500 x = 000500 x = 005

500 x = 010500 x = 015

30

00

10

00

minus10

minus30minus10

minus70

00

1070

00

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus3

times10minus7

times10minus4

times10minus5

(b)

minus20 0 20 minus20 0 20

minus20 0 20minus20 0 20

700 x = 000700 x = 005

700 x = 010700 x = 015

minus50

00

50

minus50

00

50

minus20

00

20

minus60

00

60

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus6

times10minus6

times10minus8

times10minus5

(c)

minus20 0 20 minus20 0 20

minus20 0 20 minus20 0 20

900 x = 005

900 x = 010900 x = 015

900 x = 000

minus10

10

minus10

00

00 00

10

minus50

00

50

minus30

30

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus6 times10

minus7

times10minus5

times10minus7

(d)

Figure 6 119868-119881 curves of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at different temperatures (a) 300∘C (b) 500∘C (c) 700∘C and

(d) 900∘C

to be dissolved resulting in the presence of Dy3+ ions atgrain boundaries at higher dopant concentration On theother hand low sintering leads to incomplete crystallizationhowever crystallization is prominent at higher sintering tem-perature [19] The value of dielectric constant in the presentcase is affected by oxidation state of metallic ions methodof synthesis and also the solubility of Dy3+ ion This aspectwas studied for nickel ferrite system [20] Method of syn-thesis plays an important role in determining the dielectric

properties Synthesis routes which involve comparatively lowheat treatment exhibit higher value of dielectric constantand high value of dielectric loss due to presence of organicfree radicals and metastable phases This type of behaviourwas studied by Singh et al [20] Coprecipitation methodrequires comparatively higher value of thermal treatmentthan the nitrate route This may be one reason for changein the dielectric constant [8] Another issue is the solubilityof rare earth ions in the ferrite matrix The rare earth ions

Journal of Nanoscience 9

with larger ionic radii have limited solubility in the latticeThe trace amount of the phase which could not be detectedby XRD such as the presence of Dy3+ ions on grain bound-aries may take part in polarization processes and may causean increase in the dielectric constant of the materials

35 Dielectric Loss Dielectric tangent loss (tan 120575) ofCoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) was calculated

using the relation [16]

tan 120575 = 1205761015840

12057610158401015840 (2)

where 12057610158401015840 is the imaginary part of the dielectric constant andis a measure of the absorption of energy by the dielectricmaterial from the alternating field 120575 is the loss angle and 1205761015840is the real part of the dielectric constant The dielectric losstangent versus frequency is shown in Figure 5 The valuesof the dielectric tangent loss (tan 120575) at different sinteringtemperature are tabulated in Table 5 The dielectric tangentloss (tan 120575) decreases with increase in the frequency andthen becomes constant at higher frequencies for each sampleThe value of dielectric tangent loss (tan 120575) depends on anumber of factors such as stoichiometry Fe+2 content andstructural homogeneity which in turn depend on the com-position and synthesis methods The decrease in loss tangentwith frequency may be attributed to the Maxwell-Wagnerpolarization [17] and conduction mechanism in ferritesThe dielectric loss tangent (tan 120575) changes with increase inthe dysprosium (Dy3+) concentration in cobalt ferrite Anincrease in the dielectric loss tangent was observed for thecase of undoped cobalt ferrite sintered at 700 and 900∘C

36 I-VCharacteristic Theelectrical resistivity of the sampleswas calculated using the formula

120588 = 119877

119860

119871

(3)

where 119871 is the thickness 119877 is the resistance and 119860 is thearea (119860 = 1205871199032) of the pellet Figures 6(a)ndash6(d) showthe I-V characteristics of the samples sintered at differenttemperatures The value of electrical resistivity at roomtemperature is tabulated in Table 6 The electrical resistivitydepends upon the crystal structure and composition of thematerials It changes with the increase in the dysprosium(Dy3+) concentration In the present case of CoFe

2minus119909Dy119909O4

(119909 = 000 005 010 and 015) samples it varies in therange of 18 times 105 to 162 times 109Ω-cm for different sinteringtemperatures The electrical resistivity of MnndashZnndashCe ferriteshas also been reported in the range of 14 times 105 to 43 times108Ω-cm [21] However other reports show the electricalresistivity in the range 64 times 105 to 3331 times 106Ω-cm [8] Thetemperature variation of resistivity of these materials is inprogress

4 Conclusions

The XRD TEM FTIR dielectric constant dielectric tangentloss and electrical behaviour of CoFe

2minus119909Dy119909O4(119909 = 000

005 010 and 015) was studied In the present case the bandpositions of FTIR appearing at the higher wave number(ie ]

1= 500ndash600 cmminus1) are assigned to the tetrahedral

complexes while lower wave number (]2= 400ndash450 cmminus1)

is assigned to the octahedral complexes This shows theformation of pure spinel structure of dysprosium dopedcobalt ferrite The dielectric constant of the dysprosiumdoped cobalt ferrite (CoFe

2minus119909Dy119909O4) in general decreases

with the increase in the frequency However some deviationwas observed from this usual behaviour For the samplesintered at 300∘C the dielectric constant is almost unchangedwith frequency at the particular concentrations of 119909 = 000and 005 Similar result is obtained for the sample sintered at500∘C (119909 = 010 015) 700∘C (119909 = 005 010 and 015) and900∘C (119909 = 005 010) The values of electrical resistivity ofthe materials are in the range of 105ndash109Ω-cm which may besuitable for the high frequency applicationsThe high value ofdielectric constant is useful in capacitor dielectrics The lowvalue of dielectric constant is used as microwave absorbers inhigh frequency applications In the present study the differentcompositions of the materials are suitable for both low andhigh dielectric constant applications

Conflict of Interests

The authors declare that they have no conflict of interestsregarding the publication of this paper

Acknowledgment

Hemaunt Kumar is thankful to Dr Mukul Gupta (UGCDAECSR Indore Centre) for the keen interest and suggestions inXRD measurements and also thankful to Dr Ranjan KumarSingh (Department of Physics BHU) for providing the FTIRfacilities

References

[1] S Gubbala H Nathani K Koziol and R D K Misra ldquoMag-netic properties of nanocrystalline NindashZn ZnndashMn and NindashMn ferrites synthesized by reverse micelle techniquerdquo PhysicaB Condensed Matter vol 348 no 1ndash4 pp 317ndash328 2004

[2] B Viswanathan and V R K Murthy Ferrite Materials Scienceand Technology Narosa New Delhi India 1990

[3] J-G Lee J Y Park and C S Kim ldquoGrowth of ultra-finecobalt ferrite particles by a solndashgel method and their magneticpropertiesrdquo Journal ofMaterials Science vol 33 no 15 pp 3965ndash3968 1998

[4] S N Okuno S Hanshimoto and K Inomata ldquoPreferredcrystal orientation of cobalt ferrite thin films induced by ionbombardment during deposition rdquo Journal of Applied Physicsvol 71 no 12 pp 5926ndash5929 1992

[5] H R C S Andradea L M Searaa and N D S MohallemaldquoSynthesis and characterization of BaTiO

3CoFe

2O4thin filmsrdquo

MRS Proceedings vol 1368 2011

[6] G Sathishkumar C Venkataraju and K Sivakumar ldquoSynthesisstructural and dielectric studies of nickel substituted cobalt-zinc

10 Journal of Nanoscience

ferriterdquo Materials Sciences and Applications vol 1 pp 19ndash242010

[7] G D Dwivedi K F Tseng C L Chan et al ldquoSignature offerroelectricity in magnetically ordered Mo-doped CoFe

2O4rdquo

Physical Review B CondensedMatter andMaterials Physics vol82 Article ID 134428 2010

[8] P Kumar S K Sharma andM Singh ldquoEffect of La3+ doping onthe electric dielectric and magnetic properties of cobalt ferriteprocessed by co-precipitation techniquerdquo Journal of Alloys andCompounds vol 508 no 1 pp 115ndash118 2010

[9] E Pervaiz and I H Gul ldquoStructural electrical and magneticstudies of Gd3+ doped cobalt ferrite nanoparticlesrdquo Interna-tional Journal of Current Engineering and Technology vol 2 pp377ndash387 2012

[10] M L Kahn and Z J Zhang ldquoSynthesis andmagnetic propertiesof CoFe

2O4spinel ferrite nanoparticles doped with lanthanide

ionsrdquoApplied Physics Letters vol 78 no 23 pp 3651ndash3653 2001[11] XMeng H Li J Chen L Mei KWang and X Li ldquoMossbauer

study of cobalt ferrite nanocrystals substituted with rare-earthY3+ ionsrdquo Journal ofMagnetism andMagneticMaterials vol 321no 9 pp 1155ndash1158 2009

[12] A T Raghavender R G Kulkarni and KM Jadhav ldquoMagneticproperties of mixed cobalt-aluminum ferrite nanoparticlesrdquoChinese Journal of Physics vol 48 no 4 pp 512ndash522 2010

[13] R M Mohamed M M Rashad F A Haraz and W Sig-mund ldquoStructure and magnetic properties of nanocrystallinecobalt ferrite powders synthesized using organic acid precursormethodrdquo Journal ofMagnetism andMagneticMaterials vol 322no 14 pp 2058ndash2064 2010

[14] M Gharagozlou ldquoSynthesis and characterization of nanocrys-talline magnetic pigment via coordinated precursorsrdquo Progressin Color Colorants and Coatings vol 2 no 1 pp 35ndash43 2009

[15] M A Ahmed E Ateia and F M Salem ldquoSpectroscopic andelectrical properties of MgndashTi ferrite doped with different rare-earth elementsrdquo Physica B Condensed Matter vol 381 no 1-2pp 144ndash155 2006

[16] K M Batoo ldquoStructural and electrical properties of Cu dopedNiFe2O4nanoparticles prepared through modified citrate gel

methodrdquo Journal of Physics and Chemistry of Solids vol 72 no12 pp 1400ndash1407 2011

[17] J C Maxwell A Treatise on Electricity and Magnetisim vol 1Oxford University Press New York NY USA 1973

[18] K W Wanger ldquoZur theorie der unvollkommenen dilektrikardquoAnnalen der Physik vol 345 no 5 pp 817ndash855 1913

[19] J P Singh C L Chen C L Dong et al ldquoEffect of intermediateannealing on the structural electrical and dielectric propertiesof zinc ferrite an XANES investigationrdquo Science of AdvancedMaterials vol 5 no 2 pp 171ndash181 2013

[20] J P Singh G Dixit R C Srivastava H M Agrawal andK Asokan ldquoLooking for the possibility of multiferroism inNiGd

004Fe196

O4nanoparticle systemrdquo Journal of Physics D

Applied Physics vol 44 no 43 Article ID 435306 2011[21] D Ravinder and B R Kumar ldquoElectrical conductivity of cerium

substitutedMnndashZn ferritesrdquoMaterials Letters vol 57 no 11 pp1738ndash1742 2003

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Journal of Nanoscience 5

Table 3 FTIR data of CoFe2minusxDyxO4 samples sintered at 300 500 700 and 900∘C

Samples 300∘C 500∘C 700∘C 900∘C]1(cmminus1) ]

2(cmminus1) ]

1(cmminus1) ]

2(cmminus1) ]

1(cmminus1) ]

2(cmminus1) ]

1(cmminus1) ]

2(cmminus1)

119909 = 000 567 403 553 410 567 410 560 417119909 = 005 574 417 581 411 574 417 581 417119909 = 010 581 424 594 430 584 417 587 424119909 = 015 594 424 595 437 587 424 594 430

Table 4 Dielectric constant of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) at different sintering temperatures

Samples FrequencyDielectric constant (1205761015840) at different sintering temperatures

300∘C 500∘C 700∘C 900∘C

119909 = 000

75 kHz 180 1127 834 3441MHz 177 1370 1017 3855MHz 173 1559 1143 473

119909 = 005

75 kHz 248 391 567 1491MHz 246 273 567 1495MHz 241 242 557 146

119909 = 010

75 kHz 495 293 267 2201MHz 297 282 263 2205MHz 276 274 257 216

119909 = 015

75 kHz 245 160 183 6921MHz 160 151 180 6795MHz 171 146 183 665

and more narrower with increasing sintering temperaturewhich is due to the grain growth of the particles with increasein sintering temperature The band positions of dysprosiumdoped cobalt ferrite sintered at 300∘C are in the range of567 cmminus1 to 594 cmminus1 for ]

1and 403 cmminus1 to 424 cmminus1 for ]

2

The band positions of the samples sintered 500∘C are in therange of 553 cmminus1 to 595 cmminus1 for ]

1and 410 cmminus1 to 437 cmminus1

for ]2 The band positions of the samples sintered 700∘C are

in the range 567 cmminus1 to 587 cmminus1 for ]1and 410 cmminus1 to

424 cmminus1 for ]2 The band positions of the samples sintered

900∘C are in the range of 560 cmminus1 to 594 cmminus1 for ]1and

417 cmminus1 to 430 cmminus1 for ]2 The vibrational band positions

for all the samples are shown in Table 3 It is observed thatsubstitution of Fe3+ by Dy3+ causes shifting of band positions(Fe3+ndashO2minus) towards higher frequency side due to increasedbond length at B-sites and lattice distortionThis also suggeststhe occupancy of Dy3+ at B-sites

34 Dielectric Behaviour The dielectric constant 1205761015840 of dys-prosium doped cobalt (CoFe

2minus119909Dy119909O4) ferrite has been esti-

mated from capacitance 119862 of the pellets using the formulagiven below [16]

1205761015840=

119862119889

1205760119860

(1)

where 119889 is the thickness of the pellets 119860 is the cross-sectional area in m2 and 120576

0is the permittivity of free space

The variation of dielectric constant against frequency fordifferent samples is shown in Figure 4The values of dielectricconstant are shown in Table 4 The dielectric constant of thedysprosium doped cobalt ferrite (CoFe

2minus119909Dy119909O4) in general

decreases with the increase in the frequency However in thepresent case some deviation was observed from this usualbehaviour For the sample sintered at 300∘C the dielectricconstant is almost unchanged with the frequency at theparticular concentrations of 119909 = 000 and 005 Similar resultis obtained for the sample sintered at 500∘C (119909 = 010 015)700∘C (119909 = 005 010 and 015) and 900∘C (119909 = 005 010)An increase in the dielectric constant was observed for theundoped cobalt ferrite sintered at 500 700 and 900∘C Thedecrease of dielectric constant with increasing frequency isdue to the fact that above certain frequency of the electricfield the electron exchange between Fe2+ and Fe3+ ion cannotfollow the variation of electric fieldThe space charge carriersin a dielectric material require a finite time to line up theiraxes parallel to the direction of the applied electric field If thefrequency of the field increases a point is reached when thespace charge carriers cannot cope up with the applied fieldAs a result the dielectric constant of thesematerials decreasesAs the frequency of the field continuously increases at somestage the space charge polarization would barely have started

6 Journal of Nanoscience

0 1 2 3 4

1600

1400

1200

1000

800

600

400

200

5

1100

1000

900

800

700

600

500

400

300

200

700

600

500

400

300

200

500

450

400

350

300

250

200

150

500 x = 000

500 x = 005

500 x = 010

500 x = 015

700 x = 000

700 x = 005

700 x = 010

700 x = 015

900 x = 000

900 x = 005

900 x = 010

900 x = 015

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)

Die

lect

ric co

nsta

nt

Die

lect

ric co

nsta

ntD

iele

ctric

cons

tant

Die

lect

ric co

nsta

nt

300 x = 000

300 x = 005

300 x = 010

300 x = 015

0 1 2 3 4 5

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)times106

times106

times106

times106

Figure 4 Dielectric constant of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at 300 500 700 and 900∘C

Table 5 Dielectric loss tangent (tan 120575) of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) at different sintering temperatures

Samples Frequency Dielectric tangent loss (tan 120575) at different sintering temperatures300∘C 500∘C 700∘C 900∘C

119909 = 000

75 kHz 0037 0045 0034 00281MHz 0005 0158 0151 01595MHz 0001 0072 0067 0118

119909 = 005

75 kHz 0010 179 00005 000021MHz 0001 0253 00002 000015MHz 0001 00136 00001 0001

119909 = 010

75 kHz 2006 0195 0041 000091MHz 0343 0022 000481 000075MHz 0073 0005 0003 00006

119909 = 015

75 kHz 1644 0159 0051 003951MHz 0222 0026 000481 0004565MHz 0142 0001 0003 00107

Journal of Nanoscience 7

700 x = 000

700 x = 005

700 x = 010

700 x = 015

900 x = 000

900 x = 005

900 x = 010

900 x = 015

0 1 2 3 4 5

500 x = 000

500 x = 005

500 x = 010

500 x = 015

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)

300 x = 000

300 x = 005

300 x = 010

300 x = 015

18

15

12

09

06

03

00

018 016

012

008

004

000

015

012

009

006

003

000

20

15

10

05

00

Die

lect

ric lo

ssD

iele

ctric

loss

Die

lect

ric lo

ssD

iele

ctric

loss

0 1 2 3 4 5

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)times106

times106

times106

times106

Figure 5 Dielectric loss in CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at 300 500 700 and 900∘C

Table 6 Electrical resistivity (120588) of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) at different sintering temperatures

Samples Electrical resistivity (Ω-cm) at different sintering temperatures300∘C 500∘C 700∘C 900∘C

119909 = 000 176 times 107

587 times 107

807 times 106

188 times 106

119909 = 005 683 times 107

18 times 105

787 times 108

162 times 109

119909 = 010 626 times 107

631 times 105

495 times 106

116 times 108

119909 = 015 1245 times 107

2568 times 105

2437 times 106

684 times 106

to move before the field reverses and makes virtually nocontribution to the polarization and hence to dielectricThe increase in dielectric constant with frequency may bedue to resonance effect The resonance may arise due tothe matching of the frequency of charge transfer betweenFe2+ harr Fe3+ ions and that of the applied electric fieldSimilar increase in the dielectric constant was obtained forthe La doped cobalt ferrite [8 17 18]The change in dielectricconstant with increasing dysprosium concentration may be

due to the migration of the Fe3+ ions from octahedral site totetrahedral site A similar behaviour was reported in case ofthe nickel substituted CondashZn ferrite [6] It has been reportedthat dielectric properties of materials are sensitive to themethod of synthesis microstructure and crystallite size Inthe present case two factors which have dominant effectare sintering temperature and concentration of dopant ionsAt lower concentration Dy3+ ions are dissolved in spinellattice however at higher concentration these ions cease

8 Journal of Nanoscience

minus70

00

70

minus150

000

150

minus20 0 20

minus20 0 20

300 x = 000

300 x = 010

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

00minus20 0 20

300 x = 005

Voltage (V)Curr

ent (I)

minus10

10

300 x = 015

00

Curr

ent (I)

minus10

10

minus20 0 20

Voltage (V)

times10minus6

times10minus6

times10minus6

times10minus6

(a)

minus20 0 20 minus20 0 20

minus20 0 20 minus20 0 20

500 x = 000500 x = 005

500 x = 010500 x = 015

30

00

10

00

minus10

minus30minus10

minus70

00

1070

00

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus3

times10minus7

times10minus4

times10minus5

(b)

minus20 0 20 minus20 0 20

minus20 0 20minus20 0 20

700 x = 000700 x = 005

700 x = 010700 x = 015

minus50

00

50

minus50

00

50

minus20

00

20

minus60

00

60

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus6

times10minus6

times10minus8

times10minus5

(c)

minus20 0 20 minus20 0 20

minus20 0 20 minus20 0 20

900 x = 005

900 x = 010900 x = 015

900 x = 000

minus10

10

minus10

00

00 00

10

minus50

00

50

minus30

30

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus6 times10

minus7

times10minus5

times10minus7

(d)

Figure 6 119868-119881 curves of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at different temperatures (a) 300∘C (b) 500∘C (c) 700∘C and

(d) 900∘C

to be dissolved resulting in the presence of Dy3+ ions atgrain boundaries at higher dopant concentration On theother hand low sintering leads to incomplete crystallizationhowever crystallization is prominent at higher sintering tem-perature [19] The value of dielectric constant in the presentcase is affected by oxidation state of metallic ions methodof synthesis and also the solubility of Dy3+ ion This aspectwas studied for nickel ferrite system [20] Method of syn-thesis plays an important role in determining the dielectric

properties Synthesis routes which involve comparatively lowheat treatment exhibit higher value of dielectric constantand high value of dielectric loss due to presence of organicfree radicals and metastable phases This type of behaviourwas studied by Singh et al [20] Coprecipitation methodrequires comparatively higher value of thermal treatmentthan the nitrate route This may be one reason for changein the dielectric constant [8] Another issue is the solubilityof rare earth ions in the ferrite matrix The rare earth ions

Journal of Nanoscience 9

with larger ionic radii have limited solubility in the latticeThe trace amount of the phase which could not be detectedby XRD such as the presence of Dy3+ ions on grain bound-aries may take part in polarization processes and may causean increase in the dielectric constant of the materials

35 Dielectric Loss Dielectric tangent loss (tan 120575) ofCoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) was calculated

using the relation [16]

tan 120575 = 1205761015840

12057610158401015840 (2)

where 12057610158401015840 is the imaginary part of the dielectric constant andis a measure of the absorption of energy by the dielectricmaterial from the alternating field 120575 is the loss angle and 1205761015840is the real part of the dielectric constant The dielectric losstangent versus frequency is shown in Figure 5 The valuesof the dielectric tangent loss (tan 120575) at different sinteringtemperature are tabulated in Table 5 The dielectric tangentloss (tan 120575) decreases with increase in the frequency andthen becomes constant at higher frequencies for each sampleThe value of dielectric tangent loss (tan 120575) depends on anumber of factors such as stoichiometry Fe+2 content andstructural homogeneity which in turn depend on the com-position and synthesis methods The decrease in loss tangentwith frequency may be attributed to the Maxwell-Wagnerpolarization [17] and conduction mechanism in ferritesThe dielectric loss tangent (tan 120575) changes with increase inthe dysprosium (Dy3+) concentration in cobalt ferrite Anincrease in the dielectric loss tangent was observed for thecase of undoped cobalt ferrite sintered at 700 and 900∘C

36 I-VCharacteristic Theelectrical resistivity of the sampleswas calculated using the formula

120588 = 119877

119860

119871

(3)

where 119871 is the thickness 119877 is the resistance and 119860 is thearea (119860 = 1205871199032) of the pellet Figures 6(a)ndash6(d) showthe I-V characteristics of the samples sintered at differenttemperatures The value of electrical resistivity at roomtemperature is tabulated in Table 6 The electrical resistivitydepends upon the crystal structure and composition of thematerials It changes with the increase in the dysprosium(Dy3+) concentration In the present case of CoFe

2minus119909Dy119909O4

(119909 = 000 005 010 and 015) samples it varies in therange of 18 times 105 to 162 times 109Ω-cm for different sinteringtemperatures The electrical resistivity of MnndashZnndashCe ferriteshas also been reported in the range of 14 times 105 to 43 times108Ω-cm [21] However other reports show the electricalresistivity in the range 64 times 105 to 3331 times 106Ω-cm [8] Thetemperature variation of resistivity of these materials is inprogress

4 Conclusions

The XRD TEM FTIR dielectric constant dielectric tangentloss and electrical behaviour of CoFe

2minus119909Dy119909O4(119909 = 000

005 010 and 015) was studied In the present case the bandpositions of FTIR appearing at the higher wave number(ie ]

1= 500ndash600 cmminus1) are assigned to the tetrahedral

complexes while lower wave number (]2= 400ndash450 cmminus1)

is assigned to the octahedral complexes This shows theformation of pure spinel structure of dysprosium dopedcobalt ferrite The dielectric constant of the dysprosiumdoped cobalt ferrite (CoFe

2minus119909Dy119909O4) in general decreases

with the increase in the frequency However some deviationwas observed from this usual behaviour For the samplesintered at 300∘C the dielectric constant is almost unchangedwith frequency at the particular concentrations of 119909 = 000and 005 Similar result is obtained for the sample sintered at500∘C (119909 = 010 015) 700∘C (119909 = 005 010 and 015) and900∘C (119909 = 005 010) The values of electrical resistivity ofthe materials are in the range of 105ndash109Ω-cm which may besuitable for the high frequency applicationsThe high value ofdielectric constant is useful in capacitor dielectrics The lowvalue of dielectric constant is used as microwave absorbers inhigh frequency applications In the present study the differentcompositions of the materials are suitable for both low andhigh dielectric constant applications

Conflict of Interests

The authors declare that they have no conflict of interestsregarding the publication of this paper

Acknowledgment

Hemaunt Kumar is thankful to Dr Mukul Gupta (UGCDAECSR Indore Centre) for the keen interest and suggestions inXRD measurements and also thankful to Dr Ranjan KumarSingh (Department of Physics BHU) for providing the FTIRfacilities

References

[1] S Gubbala H Nathani K Koziol and R D K Misra ldquoMag-netic properties of nanocrystalline NindashZn ZnndashMn and NindashMn ferrites synthesized by reverse micelle techniquerdquo PhysicaB Condensed Matter vol 348 no 1ndash4 pp 317ndash328 2004

[2] B Viswanathan and V R K Murthy Ferrite Materials Scienceand Technology Narosa New Delhi India 1990

[3] J-G Lee J Y Park and C S Kim ldquoGrowth of ultra-finecobalt ferrite particles by a solndashgel method and their magneticpropertiesrdquo Journal ofMaterials Science vol 33 no 15 pp 3965ndash3968 1998

[4] S N Okuno S Hanshimoto and K Inomata ldquoPreferredcrystal orientation of cobalt ferrite thin films induced by ionbombardment during deposition rdquo Journal of Applied Physicsvol 71 no 12 pp 5926ndash5929 1992

[5] H R C S Andradea L M Searaa and N D S MohallemaldquoSynthesis and characterization of BaTiO

3CoFe

2O4thin filmsrdquo

MRS Proceedings vol 1368 2011

[6] G Sathishkumar C Venkataraju and K Sivakumar ldquoSynthesisstructural and dielectric studies of nickel substituted cobalt-zinc

10 Journal of Nanoscience

ferriterdquo Materials Sciences and Applications vol 1 pp 19ndash242010

[7] G D Dwivedi K F Tseng C L Chan et al ldquoSignature offerroelectricity in magnetically ordered Mo-doped CoFe

2O4rdquo

Physical Review B CondensedMatter andMaterials Physics vol82 Article ID 134428 2010

[8] P Kumar S K Sharma andM Singh ldquoEffect of La3+ doping onthe electric dielectric and magnetic properties of cobalt ferriteprocessed by co-precipitation techniquerdquo Journal of Alloys andCompounds vol 508 no 1 pp 115ndash118 2010

[9] E Pervaiz and I H Gul ldquoStructural electrical and magneticstudies of Gd3+ doped cobalt ferrite nanoparticlesrdquo Interna-tional Journal of Current Engineering and Technology vol 2 pp377ndash387 2012

[10] M L Kahn and Z J Zhang ldquoSynthesis andmagnetic propertiesof CoFe

2O4spinel ferrite nanoparticles doped with lanthanide

ionsrdquoApplied Physics Letters vol 78 no 23 pp 3651ndash3653 2001[11] XMeng H Li J Chen L Mei KWang and X Li ldquoMossbauer

study of cobalt ferrite nanocrystals substituted with rare-earthY3+ ionsrdquo Journal ofMagnetism andMagneticMaterials vol 321no 9 pp 1155ndash1158 2009

[12] A T Raghavender R G Kulkarni and KM Jadhav ldquoMagneticproperties of mixed cobalt-aluminum ferrite nanoparticlesrdquoChinese Journal of Physics vol 48 no 4 pp 512ndash522 2010

[13] R M Mohamed M M Rashad F A Haraz and W Sig-mund ldquoStructure and magnetic properties of nanocrystallinecobalt ferrite powders synthesized using organic acid precursormethodrdquo Journal ofMagnetism andMagneticMaterials vol 322no 14 pp 2058ndash2064 2010

[14] M Gharagozlou ldquoSynthesis and characterization of nanocrys-talline magnetic pigment via coordinated precursorsrdquo Progressin Color Colorants and Coatings vol 2 no 1 pp 35ndash43 2009

[15] M A Ahmed E Ateia and F M Salem ldquoSpectroscopic andelectrical properties of MgndashTi ferrite doped with different rare-earth elementsrdquo Physica B Condensed Matter vol 381 no 1-2pp 144ndash155 2006

[16] K M Batoo ldquoStructural and electrical properties of Cu dopedNiFe2O4nanoparticles prepared through modified citrate gel

methodrdquo Journal of Physics and Chemistry of Solids vol 72 no12 pp 1400ndash1407 2011

[17] J C Maxwell A Treatise on Electricity and Magnetisim vol 1Oxford University Press New York NY USA 1973

[18] K W Wanger ldquoZur theorie der unvollkommenen dilektrikardquoAnnalen der Physik vol 345 no 5 pp 817ndash855 1913

[19] J P Singh C L Chen C L Dong et al ldquoEffect of intermediateannealing on the structural electrical and dielectric propertiesof zinc ferrite an XANES investigationrdquo Science of AdvancedMaterials vol 5 no 2 pp 171ndash181 2013

[20] J P Singh G Dixit R C Srivastava H M Agrawal andK Asokan ldquoLooking for the possibility of multiferroism inNiGd

004Fe196

O4nanoparticle systemrdquo Journal of Physics D

Applied Physics vol 44 no 43 Article ID 435306 2011[21] D Ravinder and B R Kumar ldquoElectrical conductivity of cerium

substitutedMnndashZn ferritesrdquoMaterials Letters vol 57 no 11 pp1738ndash1742 2003

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

6 Journal of Nanoscience

0 1 2 3 4

1600

1400

1200

1000

800

600

400

200

5

1100

1000

900

800

700

600

500

400

300

200

700

600

500

400

300

200

500

450

400

350

300

250

200

150

500 x = 000

500 x = 005

500 x = 010

500 x = 015

700 x = 000

700 x = 005

700 x = 010

700 x = 015

900 x = 000

900 x = 005

900 x = 010

900 x = 015

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)

Die

lect

ric co

nsta

nt

Die

lect

ric co

nsta

ntD

iele

ctric

cons

tant

Die

lect

ric co

nsta

nt

300 x = 000

300 x = 005

300 x = 010

300 x = 015

0 1 2 3 4 5

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)times106

times106

times106

times106

Figure 4 Dielectric constant of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at 300 500 700 and 900∘C

Table 5 Dielectric loss tangent (tan 120575) of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) at different sintering temperatures

Samples Frequency Dielectric tangent loss (tan 120575) at different sintering temperatures300∘C 500∘C 700∘C 900∘C

119909 = 000

75 kHz 0037 0045 0034 00281MHz 0005 0158 0151 01595MHz 0001 0072 0067 0118

119909 = 005

75 kHz 0010 179 00005 000021MHz 0001 0253 00002 000015MHz 0001 00136 00001 0001

119909 = 010

75 kHz 2006 0195 0041 000091MHz 0343 0022 000481 000075MHz 0073 0005 0003 00006

119909 = 015

75 kHz 1644 0159 0051 003951MHz 0222 0026 000481 0004565MHz 0142 0001 0003 00107

Journal of Nanoscience 7

700 x = 000

700 x = 005

700 x = 010

700 x = 015

900 x = 000

900 x = 005

900 x = 010

900 x = 015

0 1 2 3 4 5

500 x = 000

500 x = 005

500 x = 010

500 x = 015

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)

300 x = 000

300 x = 005

300 x = 010

300 x = 015

18

15

12

09

06

03

00

018 016

012

008

004

000

015

012

009

006

003

000

20

15

10

05

00

Die

lect

ric lo

ssD

iele

ctric

loss

Die

lect

ric lo

ssD

iele

ctric

loss

0 1 2 3 4 5

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)times106

times106

times106

times106

Figure 5 Dielectric loss in CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at 300 500 700 and 900∘C

Table 6 Electrical resistivity (120588) of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) at different sintering temperatures

Samples Electrical resistivity (Ω-cm) at different sintering temperatures300∘C 500∘C 700∘C 900∘C

119909 = 000 176 times 107

587 times 107

807 times 106

188 times 106

119909 = 005 683 times 107

18 times 105

787 times 108

162 times 109

119909 = 010 626 times 107

631 times 105

495 times 106

116 times 108

119909 = 015 1245 times 107

2568 times 105

2437 times 106

684 times 106

to move before the field reverses and makes virtually nocontribution to the polarization and hence to dielectricThe increase in dielectric constant with frequency may bedue to resonance effect The resonance may arise due tothe matching of the frequency of charge transfer betweenFe2+ harr Fe3+ ions and that of the applied electric fieldSimilar increase in the dielectric constant was obtained forthe La doped cobalt ferrite [8 17 18]The change in dielectricconstant with increasing dysprosium concentration may be

due to the migration of the Fe3+ ions from octahedral site totetrahedral site A similar behaviour was reported in case ofthe nickel substituted CondashZn ferrite [6] It has been reportedthat dielectric properties of materials are sensitive to themethod of synthesis microstructure and crystallite size Inthe present case two factors which have dominant effectare sintering temperature and concentration of dopant ionsAt lower concentration Dy3+ ions are dissolved in spinellattice however at higher concentration these ions cease

8 Journal of Nanoscience

minus70

00

70

minus150

000

150

minus20 0 20

minus20 0 20

300 x = 000

300 x = 010

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

00minus20 0 20

300 x = 005

Voltage (V)Curr

ent (I)

minus10

10

300 x = 015

00

Curr

ent (I)

minus10

10

minus20 0 20

Voltage (V)

times10minus6

times10minus6

times10minus6

times10minus6

(a)

minus20 0 20 minus20 0 20

minus20 0 20 minus20 0 20

500 x = 000500 x = 005

500 x = 010500 x = 015

30

00

10

00

minus10

minus30minus10

minus70

00

1070

00

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus3

times10minus7

times10minus4

times10minus5

(b)

minus20 0 20 minus20 0 20

minus20 0 20minus20 0 20

700 x = 000700 x = 005

700 x = 010700 x = 015

minus50

00

50

minus50

00

50

minus20

00

20

minus60

00

60

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus6

times10minus6

times10minus8

times10minus5

(c)

minus20 0 20 minus20 0 20

minus20 0 20 minus20 0 20

900 x = 005

900 x = 010900 x = 015

900 x = 000

minus10

10

minus10

00

00 00

10

minus50

00

50

minus30

30

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus6 times10

minus7

times10minus5

times10minus7

(d)

Figure 6 119868-119881 curves of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at different temperatures (a) 300∘C (b) 500∘C (c) 700∘C and

(d) 900∘C

to be dissolved resulting in the presence of Dy3+ ions atgrain boundaries at higher dopant concentration On theother hand low sintering leads to incomplete crystallizationhowever crystallization is prominent at higher sintering tem-perature [19] The value of dielectric constant in the presentcase is affected by oxidation state of metallic ions methodof synthesis and also the solubility of Dy3+ ion This aspectwas studied for nickel ferrite system [20] Method of syn-thesis plays an important role in determining the dielectric

properties Synthesis routes which involve comparatively lowheat treatment exhibit higher value of dielectric constantand high value of dielectric loss due to presence of organicfree radicals and metastable phases This type of behaviourwas studied by Singh et al [20] Coprecipitation methodrequires comparatively higher value of thermal treatmentthan the nitrate route This may be one reason for changein the dielectric constant [8] Another issue is the solubilityof rare earth ions in the ferrite matrix The rare earth ions

Journal of Nanoscience 9

with larger ionic radii have limited solubility in the latticeThe trace amount of the phase which could not be detectedby XRD such as the presence of Dy3+ ions on grain bound-aries may take part in polarization processes and may causean increase in the dielectric constant of the materials

35 Dielectric Loss Dielectric tangent loss (tan 120575) ofCoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) was calculated

using the relation [16]

tan 120575 = 1205761015840

12057610158401015840 (2)

where 12057610158401015840 is the imaginary part of the dielectric constant andis a measure of the absorption of energy by the dielectricmaterial from the alternating field 120575 is the loss angle and 1205761015840is the real part of the dielectric constant The dielectric losstangent versus frequency is shown in Figure 5 The valuesof the dielectric tangent loss (tan 120575) at different sinteringtemperature are tabulated in Table 5 The dielectric tangentloss (tan 120575) decreases with increase in the frequency andthen becomes constant at higher frequencies for each sampleThe value of dielectric tangent loss (tan 120575) depends on anumber of factors such as stoichiometry Fe+2 content andstructural homogeneity which in turn depend on the com-position and synthesis methods The decrease in loss tangentwith frequency may be attributed to the Maxwell-Wagnerpolarization [17] and conduction mechanism in ferritesThe dielectric loss tangent (tan 120575) changes with increase inthe dysprosium (Dy3+) concentration in cobalt ferrite Anincrease in the dielectric loss tangent was observed for thecase of undoped cobalt ferrite sintered at 700 and 900∘C

36 I-VCharacteristic Theelectrical resistivity of the sampleswas calculated using the formula

120588 = 119877

119860

119871

(3)

where 119871 is the thickness 119877 is the resistance and 119860 is thearea (119860 = 1205871199032) of the pellet Figures 6(a)ndash6(d) showthe I-V characteristics of the samples sintered at differenttemperatures The value of electrical resistivity at roomtemperature is tabulated in Table 6 The electrical resistivitydepends upon the crystal structure and composition of thematerials It changes with the increase in the dysprosium(Dy3+) concentration In the present case of CoFe

2minus119909Dy119909O4

(119909 = 000 005 010 and 015) samples it varies in therange of 18 times 105 to 162 times 109Ω-cm for different sinteringtemperatures The electrical resistivity of MnndashZnndashCe ferriteshas also been reported in the range of 14 times 105 to 43 times108Ω-cm [21] However other reports show the electricalresistivity in the range 64 times 105 to 3331 times 106Ω-cm [8] Thetemperature variation of resistivity of these materials is inprogress

4 Conclusions

The XRD TEM FTIR dielectric constant dielectric tangentloss and electrical behaviour of CoFe

2minus119909Dy119909O4(119909 = 000

005 010 and 015) was studied In the present case the bandpositions of FTIR appearing at the higher wave number(ie ]

1= 500ndash600 cmminus1) are assigned to the tetrahedral

complexes while lower wave number (]2= 400ndash450 cmminus1)

is assigned to the octahedral complexes This shows theformation of pure spinel structure of dysprosium dopedcobalt ferrite The dielectric constant of the dysprosiumdoped cobalt ferrite (CoFe

2minus119909Dy119909O4) in general decreases

with the increase in the frequency However some deviationwas observed from this usual behaviour For the samplesintered at 300∘C the dielectric constant is almost unchangedwith frequency at the particular concentrations of 119909 = 000and 005 Similar result is obtained for the sample sintered at500∘C (119909 = 010 015) 700∘C (119909 = 005 010 and 015) and900∘C (119909 = 005 010) The values of electrical resistivity ofthe materials are in the range of 105ndash109Ω-cm which may besuitable for the high frequency applicationsThe high value ofdielectric constant is useful in capacitor dielectrics The lowvalue of dielectric constant is used as microwave absorbers inhigh frequency applications In the present study the differentcompositions of the materials are suitable for both low andhigh dielectric constant applications

Conflict of Interests

The authors declare that they have no conflict of interestsregarding the publication of this paper

Acknowledgment

Hemaunt Kumar is thankful to Dr Mukul Gupta (UGCDAECSR Indore Centre) for the keen interest and suggestions inXRD measurements and also thankful to Dr Ranjan KumarSingh (Department of Physics BHU) for providing the FTIRfacilities

References

[1] S Gubbala H Nathani K Koziol and R D K Misra ldquoMag-netic properties of nanocrystalline NindashZn ZnndashMn and NindashMn ferrites synthesized by reverse micelle techniquerdquo PhysicaB Condensed Matter vol 348 no 1ndash4 pp 317ndash328 2004

[2] B Viswanathan and V R K Murthy Ferrite Materials Scienceand Technology Narosa New Delhi India 1990

[3] J-G Lee J Y Park and C S Kim ldquoGrowth of ultra-finecobalt ferrite particles by a solndashgel method and their magneticpropertiesrdquo Journal ofMaterials Science vol 33 no 15 pp 3965ndash3968 1998

[4] S N Okuno S Hanshimoto and K Inomata ldquoPreferredcrystal orientation of cobalt ferrite thin films induced by ionbombardment during deposition rdquo Journal of Applied Physicsvol 71 no 12 pp 5926ndash5929 1992

[5] H R C S Andradea L M Searaa and N D S MohallemaldquoSynthesis and characterization of BaTiO

3CoFe

2O4thin filmsrdquo

MRS Proceedings vol 1368 2011

[6] G Sathishkumar C Venkataraju and K Sivakumar ldquoSynthesisstructural and dielectric studies of nickel substituted cobalt-zinc

10 Journal of Nanoscience

ferriterdquo Materials Sciences and Applications vol 1 pp 19ndash242010

[7] G D Dwivedi K F Tseng C L Chan et al ldquoSignature offerroelectricity in magnetically ordered Mo-doped CoFe

2O4rdquo

Physical Review B CondensedMatter andMaterials Physics vol82 Article ID 134428 2010

[8] P Kumar S K Sharma andM Singh ldquoEffect of La3+ doping onthe electric dielectric and magnetic properties of cobalt ferriteprocessed by co-precipitation techniquerdquo Journal of Alloys andCompounds vol 508 no 1 pp 115ndash118 2010

[9] E Pervaiz and I H Gul ldquoStructural electrical and magneticstudies of Gd3+ doped cobalt ferrite nanoparticlesrdquo Interna-tional Journal of Current Engineering and Technology vol 2 pp377ndash387 2012

[10] M L Kahn and Z J Zhang ldquoSynthesis andmagnetic propertiesof CoFe

2O4spinel ferrite nanoparticles doped with lanthanide

ionsrdquoApplied Physics Letters vol 78 no 23 pp 3651ndash3653 2001[11] XMeng H Li J Chen L Mei KWang and X Li ldquoMossbauer

study of cobalt ferrite nanocrystals substituted with rare-earthY3+ ionsrdquo Journal ofMagnetism andMagneticMaterials vol 321no 9 pp 1155ndash1158 2009

[12] A T Raghavender R G Kulkarni and KM Jadhav ldquoMagneticproperties of mixed cobalt-aluminum ferrite nanoparticlesrdquoChinese Journal of Physics vol 48 no 4 pp 512ndash522 2010

[13] R M Mohamed M M Rashad F A Haraz and W Sig-mund ldquoStructure and magnetic properties of nanocrystallinecobalt ferrite powders synthesized using organic acid precursormethodrdquo Journal ofMagnetism andMagneticMaterials vol 322no 14 pp 2058ndash2064 2010

[14] M Gharagozlou ldquoSynthesis and characterization of nanocrys-talline magnetic pigment via coordinated precursorsrdquo Progressin Color Colorants and Coatings vol 2 no 1 pp 35ndash43 2009

[15] M A Ahmed E Ateia and F M Salem ldquoSpectroscopic andelectrical properties of MgndashTi ferrite doped with different rare-earth elementsrdquo Physica B Condensed Matter vol 381 no 1-2pp 144ndash155 2006

[16] K M Batoo ldquoStructural and electrical properties of Cu dopedNiFe2O4nanoparticles prepared through modified citrate gel

methodrdquo Journal of Physics and Chemistry of Solids vol 72 no12 pp 1400ndash1407 2011

[17] J C Maxwell A Treatise on Electricity and Magnetisim vol 1Oxford University Press New York NY USA 1973

[18] K W Wanger ldquoZur theorie der unvollkommenen dilektrikardquoAnnalen der Physik vol 345 no 5 pp 817ndash855 1913

[19] J P Singh C L Chen C L Dong et al ldquoEffect of intermediateannealing on the structural electrical and dielectric propertiesof zinc ferrite an XANES investigationrdquo Science of AdvancedMaterials vol 5 no 2 pp 171ndash181 2013

[20] J P Singh G Dixit R C Srivastava H M Agrawal andK Asokan ldquoLooking for the possibility of multiferroism inNiGd

004Fe196

O4nanoparticle systemrdquo Journal of Physics D

Applied Physics vol 44 no 43 Article ID 435306 2011[21] D Ravinder and B R Kumar ldquoElectrical conductivity of cerium

substitutedMnndashZn ferritesrdquoMaterials Letters vol 57 no 11 pp1738ndash1742 2003

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Journal of Nanoscience 7

700 x = 000

700 x = 005

700 x = 010

700 x = 015

900 x = 000

900 x = 005

900 x = 010

900 x = 015

0 1 2 3 4 5

500 x = 000

500 x = 005

500 x = 010

500 x = 015

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)

300 x = 000

300 x = 005

300 x = 010

300 x = 015

18

15

12

09

06

03

00

018 016

012

008

004

000

015

012

009

006

003

000

20

15

10

05

00

Die

lect

ric lo

ssD

iele

ctric

loss

Die

lect

ric lo

ssD

iele

ctric

loss

0 1 2 3 4 5

Frequency (Hz)0 1 2 3 4 5

Frequency (Hz)times106

times106

times106

times106

Figure 5 Dielectric loss in CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at 300 500 700 and 900∘C

Table 6 Electrical resistivity (120588) of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) at different sintering temperatures

Samples Electrical resistivity (Ω-cm) at different sintering temperatures300∘C 500∘C 700∘C 900∘C

119909 = 000 176 times 107

587 times 107

807 times 106

188 times 106

119909 = 005 683 times 107

18 times 105

787 times 108

162 times 109

119909 = 010 626 times 107

631 times 105

495 times 106

116 times 108

119909 = 015 1245 times 107

2568 times 105

2437 times 106

684 times 106

to move before the field reverses and makes virtually nocontribution to the polarization and hence to dielectricThe increase in dielectric constant with frequency may bedue to resonance effect The resonance may arise due tothe matching of the frequency of charge transfer betweenFe2+ harr Fe3+ ions and that of the applied electric fieldSimilar increase in the dielectric constant was obtained forthe La doped cobalt ferrite [8 17 18]The change in dielectricconstant with increasing dysprosium concentration may be

due to the migration of the Fe3+ ions from octahedral site totetrahedral site A similar behaviour was reported in case ofthe nickel substituted CondashZn ferrite [6] It has been reportedthat dielectric properties of materials are sensitive to themethod of synthesis microstructure and crystallite size Inthe present case two factors which have dominant effectare sintering temperature and concentration of dopant ionsAt lower concentration Dy3+ ions are dissolved in spinellattice however at higher concentration these ions cease

8 Journal of Nanoscience

minus70

00

70

minus150

000

150

minus20 0 20

minus20 0 20

300 x = 000

300 x = 010

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

00minus20 0 20

300 x = 005

Voltage (V)Curr

ent (I)

minus10

10

300 x = 015

00

Curr

ent (I)

minus10

10

minus20 0 20

Voltage (V)

times10minus6

times10minus6

times10minus6

times10minus6

(a)

minus20 0 20 minus20 0 20

minus20 0 20 minus20 0 20

500 x = 000500 x = 005

500 x = 010500 x = 015

30

00

10

00

minus10

minus30minus10

minus70

00

1070

00

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus3

times10minus7

times10minus4

times10minus5

(b)

minus20 0 20 minus20 0 20

minus20 0 20minus20 0 20

700 x = 000700 x = 005

700 x = 010700 x = 015

minus50

00

50

minus50

00

50

minus20

00

20

minus60

00

60

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus6

times10minus6

times10minus8

times10minus5

(c)

minus20 0 20 minus20 0 20

minus20 0 20 minus20 0 20

900 x = 005

900 x = 010900 x = 015

900 x = 000

minus10

10

minus10

00

00 00

10

minus50

00

50

minus30

30

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus6 times10

minus7

times10minus5

times10minus7

(d)

Figure 6 119868-119881 curves of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at different temperatures (a) 300∘C (b) 500∘C (c) 700∘C and

(d) 900∘C

to be dissolved resulting in the presence of Dy3+ ions atgrain boundaries at higher dopant concentration On theother hand low sintering leads to incomplete crystallizationhowever crystallization is prominent at higher sintering tem-perature [19] The value of dielectric constant in the presentcase is affected by oxidation state of metallic ions methodof synthesis and also the solubility of Dy3+ ion This aspectwas studied for nickel ferrite system [20] Method of syn-thesis plays an important role in determining the dielectric

properties Synthesis routes which involve comparatively lowheat treatment exhibit higher value of dielectric constantand high value of dielectric loss due to presence of organicfree radicals and metastable phases This type of behaviourwas studied by Singh et al [20] Coprecipitation methodrequires comparatively higher value of thermal treatmentthan the nitrate route This may be one reason for changein the dielectric constant [8] Another issue is the solubilityof rare earth ions in the ferrite matrix The rare earth ions

Journal of Nanoscience 9

with larger ionic radii have limited solubility in the latticeThe trace amount of the phase which could not be detectedby XRD such as the presence of Dy3+ ions on grain bound-aries may take part in polarization processes and may causean increase in the dielectric constant of the materials

35 Dielectric Loss Dielectric tangent loss (tan 120575) ofCoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) was calculated

using the relation [16]

tan 120575 = 1205761015840

12057610158401015840 (2)

where 12057610158401015840 is the imaginary part of the dielectric constant andis a measure of the absorption of energy by the dielectricmaterial from the alternating field 120575 is the loss angle and 1205761015840is the real part of the dielectric constant The dielectric losstangent versus frequency is shown in Figure 5 The valuesof the dielectric tangent loss (tan 120575) at different sinteringtemperature are tabulated in Table 5 The dielectric tangentloss (tan 120575) decreases with increase in the frequency andthen becomes constant at higher frequencies for each sampleThe value of dielectric tangent loss (tan 120575) depends on anumber of factors such as stoichiometry Fe+2 content andstructural homogeneity which in turn depend on the com-position and synthesis methods The decrease in loss tangentwith frequency may be attributed to the Maxwell-Wagnerpolarization [17] and conduction mechanism in ferritesThe dielectric loss tangent (tan 120575) changes with increase inthe dysprosium (Dy3+) concentration in cobalt ferrite Anincrease in the dielectric loss tangent was observed for thecase of undoped cobalt ferrite sintered at 700 and 900∘C

36 I-VCharacteristic Theelectrical resistivity of the sampleswas calculated using the formula

120588 = 119877

119860

119871

(3)

where 119871 is the thickness 119877 is the resistance and 119860 is thearea (119860 = 1205871199032) of the pellet Figures 6(a)ndash6(d) showthe I-V characteristics of the samples sintered at differenttemperatures The value of electrical resistivity at roomtemperature is tabulated in Table 6 The electrical resistivitydepends upon the crystal structure and composition of thematerials It changes with the increase in the dysprosium(Dy3+) concentration In the present case of CoFe

2minus119909Dy119909O4

(119909 = 000 005 010 and 015) samples it varies in therange of 18 times 105 to 162 times 109Ω-cm for different sinteringtemperatures The electrical resistivity of MnndashZnndashCe ferriteshas also been reported in the range of 14 times 105 to 43 times108Ω-cm [21] However other reports show the electricalresistivity in the range 64 times 105 to 3331 times 106Ω-cm [8] Thetemperature variation of resistivity of these materials is inprogress

4 Conclusions

The XRD TEM FTIR dielectric constant dielectric tangentloss and electrical behaviour of CoFe

2minus119909Dy119909O4(119909 = 000

005 010 and 015) was studied In the present case the bandpositions of FTIR appearing at the higher wave number(ie ]

1= 500ndash600 cmminus1) are assigned to the tetrahedral

complexes while lower wave number (]2= 400ndash450 cmminus1)

is assigned to the octahedral complexes This shows theformation of pure spinel structure of dysprosium dopedcobalt ferrite The dielectric constant of the dysprosiumdoped cobalt ferrite (CoFe

2minus119909Dy119909O4) in general decreases

with the increase in the frequency However some deviationwas observed from this usual behaviour For the samplesintered at 300∘C the dielectric constant is almost unchangedwith frequency at the particular concentrations of 119909 = 000and 005 Similar result is obtained for the sample sintered at500∘C (119909 = 010 015) 700∘C (119909 = 005 010 and 015) and900∘C (119909 = 005 010) The values of electrical resistivity ofthe materials are in the range of 105ndash109Ω-cm which may besuitable for the high frequency applicationsThe high value ofdielectric constant is useful in capacitor dielectrics The lowvalue of dielectric constant is used as microwave absorbers inhigh frequency applications In the present study the differentcompositions of the materials are suitable for both low andhigh dielectric constant applications

Conflict of Interests

The authors declare that they have no conflict of interestsregarding the publication of this paper

Acknowledgment

Hemaunt Kumar is thankful to Dr Mukul Gupta (UGCDAECSR Indore Centre) for the keen interest and suggestions inXRD measurements and also thankful to Dr Ranjan KumarSingh (Department of Physics BHU) for providing the FTIRfacilities

References

[1] S Gubbala H Nathani K Koziol and R D K Misra ldquoMag-netic properties of nanocrystalline NindashZn ZnndashMn and NindashMn ferrites synthesized by reverse micelle techniquerdquo PhysicaB Condensed Matter vol 348 no 1ndash4 pp 317ndash328 2004

[2] B Viswanathan and V R K Murthy Ferrite Materials Scienceand Technology Narosa New Delhi India 1990

[3] J-G Lee J Y Park and C S Kim ldquoGrowth of ultra-finecobalt ferrite particles by a solndashgel method and their magneticpropertiesrdquo Journal ofMaterials Science vol 33 no 15 pp 3965ndash3968 1998

[4] S N Okuno S Hanshimoto and K Inomata ldquoPreferredcrystal orientation of cobalt ferrite thin films induced by ionbombardment during deposition rdquo Journal of Applied Physicsvol 71 no 12 pp 5926ndash5929 1992

[5] H R C S Andradea L M Searaa and N D S MohallemaldquoSynthesis and characterization of BaTiO

3CoFe

2O4thin filmsrdquo

MRS Proceedings vol 1368 2011

[6] G Sathishkumar C Venkataraju and K Sivakumar ldquoSynthesisstructural and dielectric studies of nickel substituted cobalt-zinc

10 Journal of Nanoscience

ferriterdquo Materials Sciences and Applications vol 1 pp 19ndash242010

[7] G D Dwivedi K F Tseng C L Chan et al ldquoSignature offerroelectricity in magnetically ordered Mo-doped CoFe

2O4rdquo

Physical Review B CondensedMatter andMaterials Physics vol82 Article ID 134428 2010

[8] P Kumar S K Sharma andM Singh ldquoEffect of La3+ doping onthe electric dielectric and magnetic properties of cobalt ferriteprocessed by co-precipitation techniquerdquo Journal of Alloys andCompounds vol 508 no 1 pp 115ndash118 2010

[9] E Pervaiz and I H Gul ldquoStructural electrical and magneticstudies of Gd3+ doped cobalt ferrite nanoparticlesrdquo Interna-tional Journal of Current Engineering and Technology vol 2 pp377ndash387 2012

[10] M L Kahn and Z J Zhang ldquoSynthesis andmagnetic propertiesof CoFe

2O4spinel ferrite nanoparticles doped with lanthanide

ionsrdquoApplied Physics Letters vol 78 no 23 pp 3651ndash3653 2001[11] XMeng H Li J Chen L Mei KWang and X Li ldquoMossbauer

study of cobalt ferrite nanocrystals substituted with rare-earthY3+ ionsrdquo Journal ofMagnetism andMagneticMaterials vol 321no 9 pp 1155ndash1158 2009

[12] A T Raghavender R G Kulkarni and KM Jadhav ldquoMagneticproperties of mixed cobalt-aluminum ferrite nanoparticlesrdquoChinese Journal of Physics vol 48 no 4 pp 512ndash522 2010

[13] R M Mohamed M M Rashad F A Haraz and W Sig-mund ldquoStructure and magnetic properties of nanocrystallinecobalt ferrite powders synthesized using organic acid precursormethodrdquo Journal ofMagnetism andMagneticMaterials vol 322no 14 pp 2058ndash2064 2010

[14] M Gharagozlou ldquoSynthesis and characterization of nanocrys-talline magnetic pigment via coordinated precursorsrdquo Progressin Color Colorants and Coatings vol 2 no 1 pp 35ndash43 2009

[15] M A Ahmed E Ateia and F M Salem ldquoSpectroscopic andelectrical properties of MgndashTi ferrite doped with different rare-earth elementsrdquo Physica B Condensed Matter vol 381 no 1-2pp 144ndash155 2006

[16] K M Batoo ldquoStructural and electrical properties of Cu dopedNiFe2O4nanoparticles prepared through modified citrate gel

methodrdquo Journal of Physics and Chemistry of Solids vol 72 no12 pp 1400ndash1407 2011

[17] J C Maxwell A Treatise on Electricity and Magnetisim vol 1Oxford University Press New York NY USA 1973

[18] K W Wanger ldquoZur theorie der unvollkommenen dilektrikardquoAnnalen der Physik vol 345 no 5 pp 817ndash855 1913

[19] J P Singh C L Chen C L Dong et al ldquoEffect of intermediateannealing on the structural electrical and dielectric propertiesof zinc ferrite an XANES investigationrdquo Science of AdvancedMaterials vol 5 no 2 pp 171ndash181 2013

[20] J P Singh G Dixit R C Srivastava H M Agrawal andK Asokan ldquoLooking for the possibility of multiferroism inNiGd

004Fe196

O4nanoparticle systemrdquo Journal of Physics D

Applied Physics vol 44 no 43 Article ID 435306 2011[21] D Ravinder and B R Kumar ldquoElectrical conductivity of cerium

substitutedMnndashZn ferritesrdquoMaterials Letters vol 57 no 11 pp1738ndash1742 2003

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

8 Journal of Nanoscience

minus70

00

70

minus150

000

150

minus20 0 20

minus20 0 20

300 x = 000

300 x = 010

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

00minus20 0 20

300 x = 005

Voltage (V)Curr

ent (I)

minus10

10

300 x = 015

00

Curr

ent (I)

minus10

10

minus20 0 20

Voltage (V)

times10minus6

times10minus6

times10minus6

times10minus6

(a)

minus20 0 20 minus20 0 20

minus20 0 20 minus20 0 20

500 x = 000500 x = 005

500 x = 010500 x = 015

30

00

10

00

minus10

minus30minus10

minus70

00

1070

00

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus3

times10minus7

times10minus4

times10minus5

(b)

minus20 0 20 minus20 0 20

minus20 0 20minus20 0 20

700 x = 000700 x = 005

700 x = 010700 x = 015

minus50

00

50

minus50

00

50

minus20

00

20

minus60

00

60

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus6

times10minus6

times10minus8

times10minus5

(c)

minus20 0 20 minus20 0 20

minus20 0 20 minus20 0 20

900 x = 005

900 x = 010900 x = 015

900 x = 000

minus10

10

minus10

00

00 00

10

minus50

00

50

minus30

30

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

Voltage (V)Curr

ent (I)

times10minus6 times10

minus7

times10minus5

times10minus7

(d)

Figure 6 119868-119881 curves of CoFe2minus119909

Dy119909O4(119909 = 000 005 010 amp 015) sintered at different temperatures (a) 300∘C (b) 500∘C (c) 700∘C and

(d) 900∘C

to be dissolved resulting in the presence of Dy3+ ions atgrain boundaries at higher dopant concentration On theother hand low sintering leads to incomplete crystallizationhowever crystallization is prominent at higher sintering tem-perature [19] The value of dielectric constant in the presentcase is affected by oxidation state of metallic ions methodof synthesis and also the solubility of Dy3+ ion This aspectwas studied for nickel ferrite system [20] Method of syn-thesis plays an important role in determining the dielectric

properties Synthesis routes which involve comparatively lowheat treatment exhibit higher value of dielectric constantand high value of dielectric loss due to presence of organicfree radicals and metastable phases This type of behaviourwas studied by Singh et al [20] Coprecipitation methodrequires comparatively higher value of thermal treatmentthan the nitrate route This may be one reason for changein the dielectric constant [8] Another issue is the solubilityof rare earth ions in the ferrite matrix The rare earth ions

Journal of Nanoscience 9

with larger ionic radii have limited solubility in the latticeThe trace amount of the phase which could not be detectedby XRD such as the presence of Dy3+ ions on grain bound-aries may take part in polarization processes and may causean increase in the dielectric constant of the materials

35 Dielectric Loss Dielectric tangent loss (tan 120575) ofCoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) was calculated

using the relation [16]

tan 120575 = 1205761015840

12057610158401015840 (2)

where 12057610158401015840 is the imaginary part of the dielectric constant andis a measure of the absorption of energy by the dielectricmaterial from the alternating field 120575 is the loss angle and 1205761015840is the real part of the dielectric constant The dielectric losstangent versus frequency is shown in Figure 5 The valuesof the dielectric tangent loss (tan 120575) at different sinteringtemperature are tabulated in Table 5 The dielectric tangentloss (tan 120575) decreases with increase in the frequency andthen becomes constant at higher frequencies for each sampleThe value of dielectric tangent loss (tan 120575) depends on anumber of factors such as stoichiometry Fe+2 content andstructural homogeneity which in turn depend on the com-position and synthesis methods The decrease in loss tangentwith frequency may be attributed to the Maxwell-Wagnerpolarization [17] and conduction mechanism in ferritesThe dielectric loss tangent (tan 120575) changes with increase inthe dysprosium (Dy3+) concentration in cobalt ferrite Anincrease in the dielectric loss tangent was observed for thecase of undoped cobalt ferrite sintered at 700 and 900∘C

36 I-VCharacteristic Theelectrical resistivity of the sampleswas calculated using the formula

120588 = 119877

119860

119871

(3)

where 119871 is the thickness 119877 is the resistance and 119860 is thearea (119860 = 1205871199032) of the pellet Figures 6(a)ndash6(d) showthe I-V characteristics of the samples sintered at differenttemperatures The value of electrical resistivity at roomtemperature is tabulated in Table 6 The electrical resistivitydepends upon the crystal structure and composition of thematerials It changes with the increase in the dysprosium(Dy3+) concentration In the present case of CoFe

2minus119909Dy119909O4

(119909 = 000 005 010 and 015) samples it varies in therange of 18 times 105 to 162 times 109Ω-cm for different sinteringtemperatures The electrical resistivity of MnndashZnndashCe ferriteshas also been reported in the range of 14 times 105 to 43 times108Ω-cm [21] However other reports show the electricalresistivity in the range 64 times 105 to 3331 times 106Ω-cm [8] Thetemperature variation of resistivity of these materials is inprogress

4 Conclusions

The XRD TEM FTIR dielectric constant dielectric tangentloss and electrical behaviour of CoFe

2minus119909Dy119909O4(119909 = 000

005 010 and 015) was studied In the present case the bandpositions of FTIR appearing at the higher wave number(ie ]

1= 500ndash600 cmminus1) are assigned to the tetrahedral

complexes while lower wave number (]2= 400ndash450 cmminus1)

is assigned to the octahedral complexes This shows theformation of pure spinel structure of dysprosium dopedcobalt ferrite The dielectric constant of the dysprosiumdoped cobalt ferrite (CoFe

2minus119909Dy119909O4) in general decreases

with the increase in the frequency However some deviationwas observed from this usual behaviour For the samplesintered at 300∘C the dielectric constant is almost unchangedwith frequency at the particular concentrations of 119909 = 000and 005 Similar result is obtained for the sample sintered at500∘C (119909 = 010 015) 700∘C (119909 = 005 010 and 015) and900∘C (119909 = 005 010) The values of electrical resistivity ofthe materials are in the range of 105ndash109Ω-cm which may besuitable for the high frequency applicationsThe high value ofdielectric constant is useful in capacitor dielectrics The lowvalue of dielectric constant is used as microwave absorbers inhigh frequency applications In the present study the differentcompositions of the materials are suitable for both low andhigh dielectric constant applications

Conflict of Interests

The authors declare that they have no conflict of interestsregarding the publication of this paper

Acknowledgment

Hemaunt Kumar is thankful to Dr Mukul Gupta (UGCDAECSR Indore Centre) for the keen interest and suggestions inXRD measurements and also thankful to Dr Ranjan KumarSingh (Department of Physics BHU) for providing the FTIRfacilities

References

[1] S Gubbala H Nathani K Koziol and R D K Misra ldquoMag-netic properties of nanocrystalline NindashZn ZnndashMn and NindashMn ferrites synthesized by reverse micelle techniquerdquo PhysicaB Condensed Matter vol 348 no 1ndash4 pp 317ndash328 2004

[2] B Viswanathan and V R K Murthy Ferrite Materials Scienceand Technology Narosa New Delhi India 1990

[3] J-G Lee J Y Park and C S Kim ldquoGrowth of ultra-finecobalt ferrite particles by a solndashgel method and their magneticpropertiesrdquo Journal ofMaterials Science vol 33 no 15 pp 3965ndash3968 1998

[4] S N Okuno S Hanshimoto and K Inomata ldquoPreferredcrystal orientation of cobalt ferrite thin films induced by ionbombardment during deposition rdquo Journal of Applied Physicsvol 71 no 12 pp 5926ndash5929 1992

[5] H R C S Andradea L M Searaa and N D S MohallemaldquoSynthesis and characterization of BaTiO

3CoFe

2O4thin filmsrdquo

MRS Proceedings vol 1368 2011

[6] G Sathishkumar C Venkataraju and K Sivakumar ldquoSynthesisstructural and dielectric studies of nickel substituted cobalt-zinc

10 Journal of Nanoscience

ferriterdquo Materials Sciences and Applications vol 1 pp 19ndash242010

[7] G D Dwivedi K F Tseng C L Chan et al ldquoSignature offerroelectricity in magnetically ordered Mo-doped CoFe

2O4rdquo

Physical Review B CondensedMatter andMaterials Physics vol82 Article ID 134428 2010

[8] P Kumar S K Sharma andM Singh ldquoEffect of La3+ doping onthe electric dielectric and magnetic properties of cobalt ferriteprocessed by co-precipitation techniquerdquo Journal of Alloys andCompounds vol 508 no 1 pp 115ndash118 2010

[9] E Pervaiz and I H Gul ldquoStructural electrical and magneticstudies of Gd3+ doped cobalt ferrite nanoparticlesrdquo Interna-tional Journal of Current Engineering and Technology vol 2 pp377ndash387 2012

[10] M L Kahn and Z J Zhang ldquoSynthesis andmagnetic propertiesof CoFe

2O4spinel ferrite nanoparticles doped with lanthanide

ionsrdquoApplied Physics Letters vol 78 no 23 pp 3651ndash3653 2001[11] XMeng H Li J Chen L Mei KWang and X Li ldquoMossbauer

study of cobalt ferrite nanocrystals substituted with rare-earthY3+ ionsrdquo Journal ofMagnetism andMagneticMaterials vol 321no 9 pp 1155ndash1158 2009

[12] A T Raghavender R G Kulkarni and KM Jadhav ldquoMagneticproperties of mixed cobalt-aluminum ferrite nanoparticlesrdquoChinese Journal of Physics vol 48 no 4 pp 512ndash522 2010

[13] R M Mohamed M M Rashad F A Haraz and W Sig-mund ldquoStructure and magnetic properties of nanocrystallinecobalt ferrite powders synthesized using organic acid precursormethodrdquo Journal ofMagnetism andMagneticMaterials vol 322no 14 pp 2058ndash2064 2010

[14] M Gharagozlou ldquoSynthesis and characterization of nanocrys-talline magnetic pigment via coordinated precursorsrdquo Progressin Color Colorants and Coatings vol 2 no 1 pp 35ndash43 2009

[15] M A Ahmed E Ateia and F M Salem ldquoSpectroscopic andelectrical properties of MgndashTi ferrite doped with different rare-earth elementsrdquo Physica B Condensed Matter vol 381 no 1-2pp 144ndash155 2006

[16] K M Batoo ldquoStructural and electrical properties of Cu dopedNiFe2O4nanoparticles prepared through modified citrate gel

methodrdquo Journal of Physics and Chemistry of Solids vol 72 no12 pp 1400ndash1407 2011

[17] J C Maxwell A Treatise on Electricity and Magnetisim vol 1Oxford University Press New York NY USA 1973

[18] K W Wanger ldquoZur theorie der unvollkommenen dilektrikardquoAnnalen der Physik vol 345 no 5 pp 817ndash855 1913

[19] J P Singh C L Chen C L Dong et al ldquoEffect of intermediateannealing on the structural electrical and dielectric propertiesof zinc ferrite an XANES investigationrdquo Science of AdvancedMaterials vol 5 no 2 pp 171ndash181 2013

[20] J P Singh G Dixit R C Srivastava H M Agrawal andK Asokan ldquoLooking for the possibility of multiferroism inNiGd

004Fe196

O4nanoparticle systemrdquo Journal of Physics D

Applied Physics vol 44 no 43 Article ID 435306 2011[21] D Ravinder and B R Kumar ldquoElectrical conductivity of cerium

substitutedMnndashZn ferritesrdquoMaterials Letters vol 57 no 11 pp1738ndash1742 2003

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Journal of Nanoscience 9

with larger ionic radii have limited solubility in the latticeThe trace amount of the phase which could not be detectedby XRD such as the presence of Dy3+ ions on grain bound-aries may take part in polarization processes and may causean increase in the dielectric constant of the materials

35 Dielectric Loss Dielectric tangent loss (tan 120575) ofCoFe2minus119909

Dy119909O4(119909 = 000 005 010 and 015) was calculated

using the relation [16]

tan 120575 = 1205761015840

12057610158401015840 (2)

where 12057610158401015840 is the imaginary part of the dielectric constant andis a measure of the absorption of energy by the dielectricmaterial from the alternating field 120575 is the loss angle and 1205761015840is the real part of the dielectric constant The dielectric losstangent versus frequency is shown in Figure 5 The valuesof the dielectric tangent loss (tan 120575) at different sinteringtemperature are tabulated in Table 5 The dielectric tangentloss (tan 120575) decreases with increase in the frequency andthen becomes constant at higher frequencies for each sampleThe value of dielectric tangent loss (tan 120575) depends on anumber of factors such as stoichiometry Fe+2 content andstructural homogeneity which in turn depend on the com-position and synthesis methods The decrease in loss tangentwith frequency may be attributed to the Maxwell-Wagnerpolarization [17] and conduction mechanism in ferritesThe dielectric loss tangent (tan 120575) changes with increase inthe dysprosium (Dy3+) concentration in cobalt ferrite Anincrease in the dielectric loss tangent was observed for thecase of undoped cobalt ferrite sintered at 700 and 900∘C

36 I-VCharacteristic Theelectrical resistivity of the sampleswas calculated using the formula

120588 = 119877

119860

119871

(3)

where 119871 is the thickness 119877 is the resistance and 119860 is thearea (119860 = 1205871199032) of the pellet Figures 6(a)ndash6(d) showthe I-V characteristics of the samples sintered at differenttemperatures The value of electrical resistivity at roomtemperature is tabulated in Table 6 The electrical resistivitydepends upon the crystal structure and composition of thematerials It changes with the increase in the dysprosium(Dy3+) concentration In the present case of CoFe

2minus119909Dy119909O4

(119909 = 000 005 010 and 015) samples it varies in therange of 18 times 105 to 162 times 109Ω-cm for different sinteringtemperatures The electrical resistivity of MnndashZnndashCe ferriteshas also been reported in the range of 14 times 105 to 43 times108Ω-cm [21] However other reports show the electricalresistivity in the range 64 times 105 to 3331 times 106Ω-cm [8] Thetemperature variation of resistivity of these materials is inprogress

4 Conclusions

The XRD TEM FTIR dielectric constant dielectric tangentloss and electrical behaviour of CoFe

2minus119909Dy119909O4(119909 = 000

005 010 and 015) was studied In the present case the bandpositions of FTIR appearing at the higher wave number(ie ]

1= 500ndash600 cmminus1) are assigned to the tetrahedral

complexes while lower wave number (]2= 400ndash450 cmminus1)

is assigned to the octahedral complexes This shows theformation of pure spinel structure of dysprosium dopedcobalt ferrite The dielectric constant of the dysprosiumdoped cobalt ferrite (CoFe

2minus119909Dy119909O4) in general decreases

with the increase in the frequency However some deviationwas observed from this usual behaviour For the samplesintered at 300∘C the dielectric constant is almost unchangedwith frequency at the particular concentrations of 119909 = 000and 005 Similar result is obtained for the sample sintered at500∘C (119909 = 010 015) 700∘C (119909 = 005 010 and 015) and900∘C (119909 = 005 010) The values of electrical resistivity ofthe materials are in the range of 105ndash109Ω-cm which may besuitable for the high frequency applicationsThe high value ofdielectric constant is useful in capacitor dielectrics The lowvalue of dielectric constant is used as microwave absorbers inhigh frequency applications In the present study the differentcompositions of the materials are suitable for both low andhigh dielectric constant applications

Conflict of Interests

The authors declare that they have no conflict of interestsregarding the publication of this paper

Acknowledgment

Hemaunt Kumar is thankful to Dr Mukul Gupta (UGCDAECSR Indore Centre) for the keen interest and suggestions inXRD measurements and also thankful to Dr Ranjan KumarSingh (Department of Physics BHU) for providing the FTIRfacilities

References

[1] S Gubbala H Nathani K Koziol and R D K Misra ldquoMag-netic properties of nanocrystalline NindashZn ZnndashMn and NindashMn ferrites synthesized by reverse micelle techniquerdquo PhysicaB Condensed Matter vol 348 no 1ndash4 pp 317ndash328 2004

[2] B Viswanathan and V R K Murthy Ferrite Materials Scienceand Technology Narosa New Delhi India 1990

[3] J-G Lee J Y Park and C S Kim ldquoGrowth of ultra-finecobalt ferrite particles by a solndashgel method and their magneticpropertiesrdquo Journal ofMaterials Science vol 33 no 15 pp 3965ndash3968 1998

[4] S N Okuno S Hanshimoto and K Inomata ldquoPreferredcrystal orientation of cobalt ferrite thin films induced by ionbombardment during deposition rdquo Journal of Applied Physicsvol 71 no 12 pp 5926ndash5929 1992

[5] H R C S Andradea L M Searaa and N D S MohallemaldquoSynthesis and characterization of BaTiO

3CoFe

2O4thin filmsrdquo

MRS Proceedings vol 1368 2011

[6] G Sathishkumar C Venkataraju and K Sivakumar ldquoSynthesisstructural and dielectric studies of nickel substituted cobalt-zinc

10 Journal of Nanoscience

ferriterdquo Materials Sciences and Applications vol 1 pp 19ndash242010

[7] G D Dwivedi K F Tseng C L Chan et al ldquoSignature offerroelectricity in magnetically ordered Mo-doped CoFe

2O4rdquo

Physical Review B CondensedMatter andMaterials Physics vol82 Article ID 134428 2010

[8] P Kumar S K Sharma andM Singh ldquoEffect of La3+ doping onthe electric dielectric and magnetic properties of cobalt ferriteprocessed by co-precipitation techniquerdquo Journal of Alloys andCompounds vol 508 no 1 pp 115ndash118 2010

[9] E Pervaiz and I H Gul ldquoStructural electrical and magneticstudies of Gd3+ doped cobalt ferrite nanoparticlesrdquo Interna-tional Journal of Current Engineering and Technology vol 2 pp377ndash387 2012

[10] M L Kahn and Z J Zhang ldquoSynthesis andmagnetic propertiesof CoFe

2O4spinel ferrite nanoparticles doped with lanthanide

ionsrdquoApplied Physics Letters vol 78 no 23 pp 3651ndash3653 2001[11] XMeng H Li J Chen L Mei KWang and X Li ldquoMossbauer

study of cobalt ferrite nanocrystals substituted with rare-earthY3+ ionsrdquo Journal ofMagnetism andMagneticMaterials vol 321no 9 pp 1155ndash1158 2009

[12] A T Raghavender R G Kulkarni and KM Jadhav ldquoMagneticproperties of mixed cobalt-aluminum ferrite nanoparticlesrdquoChinese Journal of Physics vol 48 no 4 pp 512ndash522 2010

[13] R M Mohamed M M Rashad F A Haraz and W Sig-mund ldquoStructure and magnetic properties of nanocrystallinecobalt ferrite powders synthesized using organic acid precursormethodrdquo Journal ofMagnetism andMagneticMaterials vol 322no 14 pp 2058ndash2064 2010

[14] M Gharagozlou ldquoSynthesis and characterization of nanocrys-talline magnetic pigment via coordinated precursorsrdquo Progressin Color Colorants and Coatings vol 2 no 1 pp 35ndash43 2009

[15] M A Ahmed E Ateia and F M Salem ldquoSpectroscopic andelectrical properties of MgndashTi ferrite doped with different rare-earth elementsrdquo Physica B Condensed Matter vol 381 no 1-2pp 144ndash155 2006

[16] K M Batoo ldquoStructural and electrical properties of Cu dopedNiFe2O4nanoparticles prepared through modified citrate gel

methodrdquo Journal of Physics and Chemistry of Solids vol 72 no12 pp 1400ndash1407 2011

[17] J C Maxwell A Treatise on Electricity and Magnetisim vol 1Oxford University Press New York NY USA 1973

[18] K W Wanger ldquoZur theorie der unvollkommenen dilektrikardquoAnnalen der Physik vol 345 no 5 pp 817ndash855 1913

[19] J P Singh C L Chen C L Dong et al ldquoEffect of intermediateannealing on the structural electrical and dielectric propertiesof zinc ferrite an XANES investigationrdquo Science of AdvancedMaterials vol 5 no 2 pp 171ndash181 2013

[20] J P Singh G Dixit R C Srivastava H M Agrawal andK Asokan ldquoLooking for the possibility of multiferroism inNiGd

004Fe196

O4nanoparticle systemrdquo Journal of Physics D

Applied Physics vol 44 no 43 Article ID 435306 2011[21] D Ravinder and B R Kumar ldquoElectrical conductivity of cerium

substitutedMnndashZn ferritesrdquoMaterials Letters vol 57 no 11 pp1738ndash1742 2003

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

10 Journal of Nanoscience

ferriterdquo Materials Sciences and Applications vol 1 pp 19ndash242010

[7] G D Dwivedi K F Tseng C L Chan et al ldquoSignature offerroelectricity in magnetically ordered Mo-doped CoFe

2O4rdquo

Physical Review B CondensedMatter andMaterials Physics vol82 Article ID 134428 2010

[8] P Kumar S K Sharma andM Singh ldquoEffect of La3+ doping onthe electric dielectric and magnetic properties of cobalt ferriteprocessed by co-precipitation techniquerdquo Journal of Alloys andCompounds vol 508 no 1 pp 115ndash118 2010

[9] E Pervaiz and I H Gul ldquoStructural electrical and magneticstudies of Gd3+ doped cobalt ferrite nanoparticlesrdquo Interna-tional Journal of Current Engineering and Technology vol 2 pp377ndash387 2012

[10] M L Kahn and Z J Zhang ldquoSynthesis andmagnetic propertiesof CoFe

2O4spinel ferrite nanoparticles doped with lanthanide

ionsrdquoApplied Physics Letters vol 78 no 23 pp 3651ndash3653 2001[11] XMeng H Li J Chen L Mei KWang and X Li ldquoMossbauer

study of cobalt ferrite nanocrystals substituted with rare-earthY3+ ionsrdquo Journal ofMagnetism andMagneticMaterials vol 321no 9 pp 1155ndash1158 2009

[12] A T Raghavender R G Kulkarni and KM Jadhav ldquoMagneticproperties of mixed cobalt-aluminum ferrite nanoparticlesrdquoChinese Journal of Physics vol 48 no 4 pp 512ndash522 2010

[13] R M Mohamed M M Rashad F A Haraz and W Sig-mund ldquoStructure and magnetic properties of nanocrystallinecobalt ferrite powders synthesized using organic acid precursormethodrdquo Journal ofMagnetism andMagneticMaterials vol 322no 14 pp 2058ndash2064 2010

[14] M Gharagozlou ldquoSynthesis and characterization of nanocrys-talline magnetic pigment via coordinated precursorsrdquo Progressin Color Colorants and Coatings vol 2 no 1 pp 35ndash43 2009

[15] M A Ahmed E Ateia and F M Salem ldquoSpectroscopic andelectrical properties of MgndashTi ferrite doped with different rare-earth elementsrdquo Physica B Condensed Matter vol 381 no 1-2pp 144ndash155 2006

[16] K M Batoo ldquoStructural and electrical properties of Cu dopedNiFe2O4nanoparticles prepared through modified citrate gel

methodrdquo Journal of Physics and Chemistry of Solids vol 72 no12 pp 1400ndash1407 2011

[17] J C Maxwell A Treatise on Electricity and Magnetisim vol 1Oxford University Press New York NY USA 1973

[18] K W Wanger ldquoZur theorie der unvollkommenen dilektrikardquoAnnalen der Physik vol 345 no 5 pp 817ndash855 1913

[19] J P Singh C L Chen C L Dong et al ldquoEffect of intermediateannealing on the structural electrical and dielectric propertiesof zinc ferrite an XANES investigationrdquo Science of AdvancedMaterials vol 5 no 2 pp 171ndash181 2013

[20] J P Singh G Dixit R C Srivastava H M Agrawal andK Asokan ldquoLooking for the possibility of multiferroism inNiGd

004Fe196

O4nanoparticle systemrdquo Journal of Physics D

Applied Physics vol 44 no 43 Article ID 435306 2011[21] D Ravinder and B R Kumar ldquoElectrical conductivity of cerium

substitutedMnndashZn ferritesrdquoMaterials Letters vol 57 no 11 pp1738ndash1742 2003

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials

Submit your manuscripts athttpwwwhindawicom

ScientificaHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CorrosionInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Polymer ScienceInternational Journal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CeramicsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CompositesJournal of

NanoparticlesJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

International Journal of

Biomaterials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

NanoscienceJournal of

TextilesHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Journal of

NanotechnologyHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal of

CrystallographyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

The Scientific World JournalHindawi Publishing Corporation httpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

CoatingsJournal of

Advances in

Materials Science and EngineeringHindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Smart Materials Research

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

MetallurgyJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

BioMed Research International

MaterialsJournal of

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Nano

materials

Hindawi Publishing Corporationhttpwwwhindawicom Volume 2014

Journal ofNanomaterials