Low-temperature magnetic properties of /iron oxide nanocomposite

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<ul><li><p>at</p><p>icoc</p><p>a, a M</p><p>Ziz</p><p>iversity, Svobody 26, 77146 Olomouc, Czech Republic</p><p>nce 2, CZ-18221 Praha 8, Czech Republic</p><p>hy</p><p>e 1</p><p>size</p><p>investigated in the temperature range 4293K by Mossbauer spectroscopy and magnetic measurements in DC and AC elds. Fe C was</p><p>structural, magnetic and high-temperature properties of a</p><p>pyrolysis of iron pentacarbonyl FeCO5 and ethyleneC2H4 gases [3]. The sample was passivated in situ by agradual increase of air in the surrounding atmosphere [1].</p><p>The physical properties measuring system PPMS 9 from</p><p>iron with the diameter around 10 nm. The diffractions fromFe3O4 were found in the powder electron diffractogram.The XRD pattern of the synthesized sample was well tted</p><p>ARTICLE IN PRESSwith orthorhombic cementite Fe3C (75wt%, mean coherencedomain length dXRD 18 nm) and Fe3O4=gFe2O3 (25wt%,dXRD 5 nm) [2].</p><p>0304-8853/$ - see front matter r 2007 Elsevier B.V. All rights reserved.</p><p>doi:10.1016/j.jmmm.2007.03.091</p><p>Corresponding author. Tel.: +420532290436; fax: +420541218657.E-mail address: david@ipm.cz (B. David).nanocrystalline Fe3C-based sample. Nevertheless, furthermagnetic measurements are needed to understand better itsmagnetic behavior.In the present article, we extend our study by employing</p><p>Mossbauer spectroscopy and magnetic measurements atlow temperatures.</p><p>2. Experimental procedure</p><p>The nanopowder has been synthesized by the CO2 laser</p><p>quantum design equipped with the P500 AC/DC magne-tometry system was used for magnetic measurements.</p><p>3. Results and discussion</p><p>The TEM analysis of the sample [1] revealed the twotypes of nanoparticles and their morphology: (a) aggre-gated Fe3C crystalline particles with coreshell structure(core: Fe3C; shell: pyrolytic carbon) with diameter around20 nm; (b) aggregated nanoparticles containing oxygen andidentied as the dominant phase in the sample (75wt%). The mean size of the Fe3C crystallites is estimated to be 20 nm. The residual</p><p>phase in the sample is probably a mixture of nanocrystalline Fe3O4, gFe2O3, and aFe2O3. Zero-eld-cooled and eld-cooled DCmeasurements as well as real and imaginary parts of AC susceptibility curves are discussed. The nanopowder exhibits superferromagnetic</p><p>behavior.</p><p>r 2007 Elsevier B.V. All rights reserved.</p><p>PACS: 81.07.Wx; 75.50.Bb; 75.50.Ts</p><p>Keywords: Fe3C; Nanopowder; Mossbauer spectroscopy; AC susceptibility; Magnetic properties</p><p>1. Introduction</p><p>In our previous articles [1,2], we have described basic</p><p>Transmission electron microscopy (TEM), X-ray diffrac-tion (XRD), infrared (IR), Raman and Mossbauer spectro-scopies were used for structural studies.3B. David , O. Schneeweiss , M.aInstitute of Physics of Materials, AS CR,</p><p>bDepartment of Experimental Physics, Palacky UncInstitute of Physics, AS CR, Na Slova</p><p>dNational Institute for Laser, Plasma, and Radiation P</p><p>Available onlin</p><p>Abstract</p><p>The magnetic properties of the Fe3C-based nanopowder syntheJournal of Magnetism and Magnetic M</p><p>Low-temperature magnetoxide nansics, P.O. Box MG-36, R-76900 Bucharest, Romania</p><p>5 March 2007</p><p>d by laser pyrolysis of ethylene and iron pentacarbonyl gases areerials 316 (2007) 422425</p><p>properties of Fe3C/ironomposite</p><p>ashlanb, E. Santavac, I. Morjand</p><p>kova 22, CZ-61662 Brno, Czech Republic</p><p>www.elsevier.com/locate/jmmm</p></li><li><p>ARTICLE IN PRESS</p><p>-10 -5 0 5 10</p><p>Velocity [mm/s]</p><p>0.94</p><p>0.96</p><p>0.98</p><p>1.00</p><p>Rela</p><p>tive tra</p><p>nsm</p><p>issio</p><p>n</p><p>0.94</p><p>0.96</p><p>0.98</p><p>1.00</p><p>at 4 K</p><p>at 293 Ka</p><p>b</p><p>Fig. 2. Mossbauer spectra for the Fe3C-based nanopowder. (a) Fe3C</p><p>component (gray ller) is the superposition of the FeG and FeS sextets.</p><p>Other components: sextet S1 (full line), distribution DIS1 (dashed line),</p><p>and doublet D1 (full line). (b) Fe3C component (gray ller) is the</p><p>superposition of the FeG and FeS sextets. FexOy component (network</p><p>ller) is a Gaussian distribution. The third component (black ller) is the</p><p>superposition of the ST1 and ST2 sextets.</p><p>Table 1</p><p>Parameters of the spectral sextets/doublets used for the tting of the</p><p>Mossbauer spectra in Fig. 1</p><p>Component BHF [T] DBHF [T] eQ [mm/s] d [mm/s] A [%]</p><p>At 293K</p><p>Fe3C : FeS 21.2 0.03 0.21 30Fe3C : FeG 20.3 0.01 0.20 60S1 17.9 0.01 0.20 3</p><p>nd MThe IR spectrum of the sample (Fig. 1a) exhibitsminimum at 602 cm1 which is characteristic for bothFe3O4 and gFe2O3 [4].The Raman spectrum of the sample (Fig. 1b) exhibits</p><p>signicant maximum at 670 cm1 which is typical forFe3O4 [4] and corresponds to its most active A1g band [5].The maxima at 220, 280 cm1 are assigned to aFe2O3traces.In the Mossbauer spectrum of our sample measured at</p><p>293K (Fig. 2a, Table 1) the Fe3C sextets dominate but thespectrum cannot be satisfactorily tted with them only.The y-iron carbide Fe3C (cementite) is orthorhombic</p><p>with space group Pnma [6]. It has the iron atoms locatedat the general site (FeG atoms) and at the special site(FeS atoms). Two times more iron atoms occupy thegeneral site than the special site. Previous studies ofbulk cementite samples led to the identication of twosimilar sextets measured at room temperature [7,8] and at4K [8]. Mossbauer spectra of nanoparticle cementitemeasured at room temperature and at 12K were alsoreported [9].Our parameters of the Fe3C sextets in the spectrum</p><p>measured at 293K agree well with those cited [8,9]. The S1sextet can be ascribed to Fe3C surface/interface. The DIS1distribution is assigned to superparamagnetic FexOyparticles interacting with Fe3C phase. The D1 doubletbelongs to Fe3 or superparamagnetic Fe3C particles.</p><p>50010001500</p><p>Wavenumber [cm-1]</p><p>Inte</p><p>nsity [a.u</p><p>]</p><p>5001000</p><p>Ramanshift [cm-1]In</p><p>tensity [a.u</p><p>]</p><p>Fig. 1. (a) Infrared spectrum and (b) Raman spectrum for the Fe3C-based</p><p>nanopowder.</p><p>B. David et al. / Journal of Magnetism aIn the low-temperature Mossbauer spectrum (Fig. 2b,Table 1) the FexOy distribution needed to t the spectrumconrmed the presence of iron oxide(s) in our sample [4].This iron oxide component could not be tted with Fe3O4sextets only [10]. In the spectra measured at various lowtemperatures, the iron oxide sextets/distribution withBHF4BHFFe3C started to appear below 100K. Theparameters of the Fe3C sextets correspond again well tothose cited [8,9]. The ST1, ST2 sextets can be assigned toFe3C surface/interface.The hysteresis loop of our sample measured at 293K</p><p>provided the values of coercivity HC 52 kA=m, remanentmagnetization sR 16Am2=kg, and saturation magneti-zation sS 102Am2=kg (at 6400 kA/m). The bulk valuefor Fe3C is sS(bulk Fe3C 130Am2=kg [11]. Corre-sponding values for the hysteresis loop of the sample-10 -5 0 5 10</p><p>agnetic Materials 316 (2007) 422425 423measured at 4K are: HC 144 kA=m, sR 34Am2=kg,and sS 122Am2=kg (at 6400 kA/m).The hysteresis loop measured at 4K after the sample was</p><p>eld-cooled (FC) in 800 kA/m was not shifted relative to</p><p>DIS1 8.8 8.0 0.02 0.42 5</p><p>D1 0.23 0.18 2</p><p>At 4K</p><p>Fe3C : FeS 25.6 0.01 0.35 29Fe3C : FeG 24.2 0.01 0.35 58ST1 21.0 0.09 0.25 3</p><p>ST2 15.9 0.15 0.24 2FexOy 48.4 8.3 0.03 0.45 8</p><p>BHF hyperne magnetic induction; DBHF width of hyperne elddistribution; eQ quadrupole shift; d isomer shift with respect to aFe; Arelative spectrum area.</p></li><li><p>the loop measured at 4K after zero-eld cooling. It meansthat our sample does not exhibit glassy dynamics [12].The zero-eld-cooled (ZFC) and FC s (8 kA/m) curves</p><p>indicate a superferromagnetic state of the sample attemperatures lower than 300K [13,14]. A collective freezingof Fe3C particles magnetic moments (superspins) takesplace during zero-eld cooling.A noticeable feature of the high eld cooling data</p><p>(Fig. 3) is the increase of s(800 kA/m) starting at 40Kduring the cooling of the sample.The measurement of the in-phase AC susceptibility (w0)</p><p>and out-of-phase AC susceptibility (w00) after cooling thesample in zero magnetic eld (Fig. 4) was repeatedlyperformed with the following results: (a) the blockingtemperature TB of superparamagnetic particles [15]taken as the absolute maximum of the w00 curve is 95K;(b) an abrupt decrease in w00 takes place at 40K (local</p><p>cally through dipoledipole interactions or directly via</p><p>I. Sandu, C.T. Fleaca, Solid State Phenom. 99100 (2004) 181.</p><p>ARTICLE IN PRESS</p><p>0 100 200 300</p><p>T [K]</p><p>0.6</p><p>0.8</p><p>1.0</p><p>1.2</p><p>1.4</p><p>1.6</p><p> (8 k</p><p>A/m</p><p>) [A</p><p>m2/k</p><p>g]</p><p>96</p><p>97</p><p>98</p><p>99</p><p>100</p><p>101</p><p>102</p><p> (800 k</p><p>A/m</p><p>) [A</p><p>m2/k</p><p>g]</p><p>ZFCin 8 kA/m</p><p>FC in 8 kA/m</p><p>FC in 800 kA /m</p><p>ZFCin 800 kA/m</p><p>Fig. 3. DC magnetization for the Fe3C-based nanopowder.</p><p>B. David et al. / Journal of Magnetism and M4240 100 200 300</p><p>T [K]</p><p>120</p><p>140</p><p>160</p><p>180</p><p>200</p><p>'[c</p><p>m3/k</p><p>g]</p><p>0.0</p><p>0.4</p><p>0.8</p><p>1.2</p><p>''[c</p><p>m3/k</p><p>g]</p><p>' '</p><p>ZFC</p><p>'</p><p>ZFC</p><p>HAC= 800 A /m</p><p>f = 1 kHzHDC= 0 A/mFig. 4. AC susceptibility for the Fe3C-based nanopowder.[4] R.M. Cornell, U. Schwertmann, The Iron Oxides, Wiley VCH</p><p>Publishers, Weinheim, 1999 (chapter 7).</p><p>[5] O.N. Shebanova, P. Lazor, J. Solid State Chem. 174 (2003) 424.</p><p>[6] E.J. Fasiska, G.A. Jeffrey, Acta Cryst. 19 (1965) 463.</p><p>[7] M. Ron, Z. Mathalone, Phys. Rev. B 4 (3) (1971) 774.</p><p>[8] G. LeCaer, J.M. Dubois, J.P. Senateur, J. Solid State Chem. 19</p><p>(1976) 19.</p><p>[9] X.X. Bi, B. Ganguly, G.P. Huffman, F.E. Huggins, M. Endo, P.C.</p><p>Eklund, J. Mater. Res. 8 (1993) 1666.</p><p>[10] C.M. Srivastava, S.N. Shringi, M.V. Babu, Phys. Stat. Sol. (A) 65</p><p>(1981) 731.</p><p>[11] R.M. Bozoroth, Ferromagnetism, D. Van Nostrand, New York,</p><p>1951.Acknowledgments</p><p>This work was supported by the Grant Agency of theCzech Republic (No. 202/04/0221), the Academy ofSciences of the Czech Republic (No. AV0Z20410507),and Ministry of Education, Youth and Sport of the CzechRepublic (No. 1M619895g201).</p><p>References</p><p>[1] B. David, O. Schneeweiss, N. Pizurova, M. Klementova, P. Bezdicka,</p><p>R. Alexandrescu, F. Dumitrache, I. Morjan, Surf. Interface Anal. 38</p><p>(4) (2006) 482.</p><p>[2] B. David, R. Zboril, M. Mashlan, T. Grygar, F. Dumitrache,</p><p>O. Schneeweiss, J. Magn. Magn. Mater. 304 (2006) e787.</p><p>[3] R. Alexandrescu, I. Morjan, F. Dumitrache, I. Voicu, I. Soare,interfaces. From ZFC/FC curves and hysteresis loops,Fe3C phase was inferred to be superferromagnetic.FexOy nanoparticles and their aggregates with uctuat-</p><p>ing magnetic moments were identied as the second phasein the sample. This phase undergoes transformation intomagnetically ordered state during cooling of the samplebelow 100K.minimum at 35K). The value of TB was observed to beAC frequency dependentit shifted to higher temperatureswith increasing frequency. The fall of w00 at 40K wasnot AC frequency dependent. It seems that the minimumof w00 at 35K can be attributed to the structural/magneticchanges in Fe3O4 at low temperatures [1620]. Thedecrease of w00 at 40K coincides with the increase ins800 kA=m at 40K in Fig. 3. It should be noted that inour case FexOy nanoparticles are aggregated into largerstructures [1].</p><p>4. Conclusions</p><p>The low-temperature magnetic properties of the Fe3C/iron oxide nanocomposite were described. Fe3C nanopar-ticles were found to be ferromagnetic and aggregated intolarger structures and covered by pyrolytic carbon. TheFe3C nanoparticles and their aggregates interact magneti-</p><p>agnetic Materials 316 (2007) 422425[12] D. Fiorani, L. Del Bianco, A.M. Testa, J. Magn. Magn. Mater. 300</p><p>(2006) 179.</p></li><li><p>[13] E. Bonetti, L. Del Bianco, D. Fiorani, D. Rinaldi, R. Caciuffo,</p><p>A. Hernando, Phys. Rev. Lett. 83 (14) (1999) 2829.</p><p>[14] O. Petracic, A. Glatz, W. Kleemann, Phys. Rev. B 70 (2004) 214432.</p><p>[15] S. Mrup, J.A. Dumesic, H. Topse, in: R.L. Cohen (Ed.),</p><p>Applications in Mossbauer Spectroscopy, vol. II, Academic Press,</p><p>New York, 1980, p. 1.</p><p>[16] V. Skumryev, H.J. Blythe, J. Cullen, J.M.D. Coey, J. Magn. Magn.</p><p>Mater. 196 (1999) 515.</p><p>[17] M. Ba"anda, A. Wiechec, D. Kim, Z. Kakol, A. Koz"owski,P. Niedziela, J. Sabol, Z. Tarnawski, J.M. Honig, Eur. Phys. J. B</p><p>43 (2005) 201.</p><p>[18] A. Kosterov, Geophys. J. Int. 154 (2003) 58.</p><p>[19] G.F. Goya, T.S. Berquo, F.C. Fonseca, M.P. Morales, J. Appl. Phys.</p><p>94 (5) (2003) 3520.</p><p>[20] O. Schneeweiss, R. Zboril, N. Pizurova, M. Mashlan, E. Petrovsky,</p><p>J. Tucek, Nanotechnology 17 (2006) 607.</p><p>ARTICLE IN PRESSB. David et al. / Journal of Magnetism and Magnetic Materials 316 (2007) 422425 425</p><p>Low-temperature magnetic properties of Fe3C/iron oxide nanocompositeIntroductionExperimental procedureResults and discussionConclusionsAcknowledgmentsReferences</p></li></ul>

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