Structural and thermodynamic properties of Fe1.12Te with multiple phase transitionsDona Cherian, S. Rößler, C. Koz, A. A. Tsirlin, U. Schwarz, S. Wirth, and Suja Elizabeth Citation: Journal of Applied Physics 115, 123912 (2014); doi: 10.1063/1.4870233 View online: http://dx.doi.org/10.1063/1.4870233 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/115/12?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Structural transitions and unusual magnetic behavior in Mn-doped Bi1−xLaxFeO3 perovskites J. Appl. Phys. 112, 084102 (2012); 10.1063/1.4759435 The effect of strontium doping on the structural and magnetic transition of YMnO3 AIP Conf. Proc. 1447, 1013 (2012); 10.1063/1.4710349 Structural and magnetic phase transition of mixed olivines Li x Fe1−y Ni y PO4 by lithium deintercalation J. Appl. Phys. 111, 07D722 (2012); 10.1063/1.3678468 Anomalous heat capacity and x-ray photoelectron spectroscopy of superconducting FeSe1/2Te1/2 J. Appl. Phys. 109, 07E122 (2011); 10.1063/1.3556682 Magnetic properties of Bi 2 FeMnO 6 : A multiferroic material with double-perovskite structure Appl. Phys. Lett. 97, 122502 (2010); 10.1063/1.3490221

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Structural and thermodynamic properties of Fe1.12Te with multiple phasetransitions

Dona Cherian,1,a) S. R€oßler,2 C. Koz,2 A. A. Tsirlin,2,3 U. Schwarz,2 S. Wirth,2

and Suja Elizabeth1

1Department of Physics, Indian Institute of Science, Bangalore 560012, India2Max Planck Institute for Chemical Physics of Solids, N€othnitzer Straße 40, 01187 Dresden, Germany3National Institute of Chemical Physics and Biophysics, 12618 Tallinn, Estonia

(Received 12 February 2014; accepted 21 March 2014; published online 31 March 2014)

The parent compound of iron chalcogenide superconductors, Fe1þyTe, with a range of excess Fe

concentrations exhibits intriguing structural and magnetic properties. Here, the interplay of

magnetic and structural properties of Fe1.12Te single crystals have been probed by low-temperature

synchrotron X-ray powder diffraction, magnetization, and specific heat measurements.

Thermodynamic measurements reveal two distinct phase transitions, considered unique to samples

possessing excess Fe content in the range of 0:11 � y � 0:13. On cooling, an antiferromagnetic

transition, TN � 57 K is observed. A closer examination of powder diffraction data suggests that

the transition at TN is not purely magnetic, but accompanied by the commencement of a structural

phase transition from tetragonal to orthorhombic symmetry. This is followed by a second

prominent first-order structural transition at TS with TS < TN , where an onset of monoclinic

distortion is observed. The results point to a strong magneto-structural coupling in this material. VC 2014AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4870233]

I. INTRODUCTION

Simple crystal structure, unique magnetic ground

states, intriguing electronic properties, structural transi-

tions, and superconductivity in substituted and pristine Fe

chalcogenides make these compounds interesting candi-

dates for the studies of condensed matter physics.1–4

Fe1þyTe is an antiferromagnetic compound whereas FeSe,

the other binary system, is a superconductor with a super-

conducting transition temperature TC � 8 K.5,6 Substitution

with other chalcogenides (Se/S) at the Te site in Fe1þyTe

induces superconductivity7,8 and the maximum TC of

15 K was observed for about 50% Se substitution.7,9,10

Even though different Fe pnictides share several common

properties,11 Fe chalcogenides possess rather different elec-

tronic and magnetic behavior.12 The parent compound,

Fe1þyTe is distinguished in its Fermi surface topology,

magnetic ground states, and structural properties.5,13

Fe1þyTe with y¼ 0.06 exhibits a prominent magneto-

structural transition at 70 K below which an antiferromag-

netic order sets.5 For y increasing up to below 0.11, the mate-

rial undergoes a first-order transition from paramagnetic

tetragonal to a commensurate antiferromagnetic monoclinic

phase. The magneto-structural transition occurs in a broad

range of temperature, approximately from 70 K to 57 K

depending on the amount of excess Fe. As Fe content

increases beyond y¼ 0.11, the paramagnetic tetragonal

phase changes into an incommensurate antiferromagnetic

orthorhombic phase14,15 at about 57 K. The magnetic propa-

gation vector is temperature dependent until a lock-in

transition occurs at a lower temperature. For y� 0.14, a sin-

gle continuous phase transition to an incommensurate

antiferromagnetic phase with orthorhombic symmetry has

been observed.16,17 The temperature-composition phase dia-

gram portrays the dependence and sensitivity of transition

temperatures to the excess Fe concentration.17,18

Although the Fe1þyTe system is relatively well investi-

gated by now, one of the issues that remains particularly

controversial is the exact nature of the magnetic and struc-

tural transitions and couplings in the intermediate composi-

tional range of 0:11 � y � 0:13. For instance, in Fe1.13Te,

the two phase transitions occur at 57 K and 46 K. In a previ-

ous report on Fe1.13Te single crystals,19 we presented pre-

liminary low-temperature synchrotron powder diffraction

data which suggested a symmetry-breaking transition

occurring only at the second transition (46 K). These data,

however, were limited to only four temperature points.

Using synchrotron powder diffraction, the composition of

the same crystal is now carefully redetermined as Fe1.12Te.

Around the same time, a neutron scattering work20 on

Fe1.10Te with similar thermodynamic properties like those

of our Fe1.12Te single crystals, reported a structural distor-

tion at 63 K followed by a magnetic transition at 57.5 K.

Later investigations17,21 on polycrystalline Fe1.12Te indi-

cated a two-step transition from a tetragonal-orthorhombic

followed by an orthorhombic-monoclinic transition upon

cooling. These results, combined with the neutron scatter-

ing data,16 suggest that the two transitions have both mag-

netic and structural components. Now, the different results

found in the polycrystalline Fe1.12Te and the powdered sin-

gle crystals of the same composition could be either due to

microstructural effects or due to the coarse temperature

grid used in Ref. 19. With the intention to resolve this issue,

here we re-examine the same sample that was used in Ref.

19 with diffraction data taken at a temperature interval of

2 K in the temperature range of 70–30 K. Further, wea)donacherian@physics.iisc.ernet.in

0021-8979/2014/115(12)/123912/6/$30.00 VC 2014 AIP Publishing LLC115, 123912-1

JOURNAL OF APPLIED PHYSICS 115, 123912 (2014)

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present a detailed analysis of the specific heat and report

the Sommerfeld coefficient, Debye temperature, and the

change in entropies at the phase transition.

II. EXPERIMENTAL

Single crystals of Fe1.12Te were grown by a modified

horizontal Bridgman method. The details of crystal growth

can be found elsewhere.19 The grown crystals were charac-

terized using Laue back scattering and powder X-ray diffrac-

tion (XRD). A composition analysis was made to verify the

homogeneous nature of the sample over a finite area by scan-

ning the surface using an electron probe microanalyzer,

JEOL-JXA-8530F. Powder XRD patterns were obtained in

the temperature range of 30 K–300 K using synchrotron

source at ID 31 at European Synchrotron Radiation Facility

(ESRF). Temperature dependent XRD patterns were recorded

by cooling the powdered crystal sample in a liquid-helium

cryostat. Measurements were made from 30 K to 70 K at inter-

vals of 2 K from a synchrotron source of wavelength

0.430459 A. Data between 75 K and 300 K were collected

using a source of wavelength 0.399928 A. XRD patterns were

refined and structural parameters and occupancy were esti-

mated. Resistivity and specific heat measurements were carried

out using a Quantum Design physical property measurement

system (PPMS). The dc magnetization was measured in a

SQUID magnetometer (Quantum Design).

III. RESULTS AND DISCUSSION

The layered structure and the inherent anion-anion

repulsion enable the as-grown Fe chalcogenide crystals to be

cleaved along the ab plane. The Laue photograph (Figure

1(a)) of cleaved Fe1.12Te illustrates the single crystalline na-

ture of the as-grown crystal. Since physical properties are

extremely sensitive to the concentration of Fe, it is necessary

to check the chemical homogeneity of the crystal employed

for this study. The sample surface was scanned using wave-

length dispersive X-ray (WDX) spectroscopy to confirm the

chemical homogeneity. The WDX surface image is pre-

sented in Figure 1(b), which shows a uniform distribution of

Fe. The lines on the top left corner are cracks formed while

cleaving. Similar colored spots are due to some pits on the

surface.

Synchrotron powder XRD data of Fe1.12Te crystals are

analyzed and the crystal structure is refined by Rietveld

method22 using FullProf code assuming a starting model

from a previous report on Fe1.04Te0.5Se0.5 (Ref. 10).

Composition of the as-grown crystals used in Ref. 19 was

also redetermined using XRD from synchrotron data and

was obtained as Fe1.12Te with a standard deviation of 0.002.

The crystals used for XRD possess two separate transitions

as discussed in Ref. 19. The transition at 57 K corresponds to

a second order transition referred to as TN and the one at

46 K is a first order transition referred to as TS. The transition

temperatures are determined from the specific heat measure-

ments (presented later). Figure 2 illustrates the refined pow-

der pattern at 70 K. The structure is tetragonal and is refined

in P4/nmm space group. The inset of Figure 2 shows the tet-

ragonal crystal structure. The structure consists of layers of

Fe square lattice with Te occupying checker board positions

above and below the Fe layer. Excess Fe occupies the 2cposition in the Te plane whose magnetic interactions play a

crucial role in lattice distortion.23 The strong magnetoelastic

coupling in Fe1þyTe and its distinguishable behavior at the

critical composition substantiate the role of subtle changes in

Fe(y). XRD data above and below TN are carefully analyzed

using Rietveld refinement in P4/nmm space group and ortho-

rhombic Pmmn space group. For 70 K, which is above TN,

the fitted peak intensities and residual of P4/nmm are consid-

erably better than Pmmn with corresponding v2 values of

1.59 and 2.1, respectively. The pattern at 54 K is better

refined in Pmmn ðv2 ¼ 1:39Þ than in P4/nmm ðv2 ¼ 1:8Þ.The matching of the fitted peaks to the observed peaks is

also taken into account. The distinction between the tetrago-

nal and orthorhombic phases becomes clearer when the tem-

perature is lowered to 50 K. At 48 K, Pmmn yields v2 ¼ 1:71

and P21/m yields v2 ¼ 1:8 indicating that Pmmn is a better

model for the crystal structure for temperatures between TN

and TS. Below TS, a monoclinic distortion should be intro-

duced in order to describe the broadening of the (101) reflec-

tion. However, the monoclinic phase alone does not provide

a complete description of the intensity at (101) and (�101).

This missing intensity is well described by a small amount

(7%) of an orthorhombic phase. For data below TS, the

refinement is performed in monoclinic phase alone and also

in a combination of P21/m and Pmmn. The latter yields a

FIG. 1. (a) Laue photograph showing diffraction spots and four fold symme-

try. (b) Fe Composition mapping done by WDX spectroscopy on a 2 mm �1.5 mm cleaved surface.

FIG. 2. XRD crystal structure refinement of 70 K data. Global v2 ¼ 1:65

and Bragg R-factor¼ 1.94. Inset shows the tetragonal crystal structure.

123912-2 Cherian et al. J. Appl. Phys. 115, 123912 (2014)

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better reliability factor and residual (for example, 44 K data

yields v2 ¼ 1:48 for the combination model, whereas a pure

monoclinic model gives v2 ¼ 1:79). The coexistence of the

orthorhombic and monoclinic phases is not unexpected,

according to the earlier observation of the phase separation

in polycrystalline Fe1.12Te.17

A closer look at the diffraction patterns reveals that

below TN, broadening of the (200) peak starts. This is sug-

gestive of the onset of an orthorhombic distortion within the

tetragonal lattice. As the temperature further falls to 52 K,

the split in peaks become more evident and the structure

transforms to the orthorhombic space group Pmmn. On fur-

ther lowering the temperature below TS, the crystal exhibits a

monoclinic distortion. The orthorhombic splitting and mono-

clinic broadening of different Bragg peaks as the temperature

is varied across the transition, are shown in Figure 3. The

(200) Bragg peak starts broadening at 54 K and splits into

(200) and (020) as the temperature is lowered. The splitting

observed below TN clearly indicates the appearance of the

orthorhombic phase below TN. Similarly, peak splittings are

observed in other sets of Bragg peaks, (101) and (011), (211)

and (121), (301) and (031), (311) and (131), and (312) and

(132). When the temperature is below TS, monoclinic broad-

ening starts for some of the above peaks, (�101), (�211)

and (�312). To account for the peak broadening of the (101)

Bragg plane, a monoclinic (�101) Bragg plane has to be

considered. The intensity mismatch between (101) and (011)

peaks also calls for a mixed phase of P21/m and Pmmn for

refinement. However, there is no clear splitting of the (112)

Bragg peak that is characteristic of a pure monoclinic phase.

This is better understood from the analysis of the full

width at half maxima (FWHM) of different Bragg peaks as a

function of temperature in Figure 4. In case of split transitions,

FWHM is estimated as the width of the overall profile com-

prising the split peaks, at half intensity of the higher peak.

Sizable changes are perceptible across the phase transition.

Below TN, FWHM of (200) and (020) increases in magnitude,

indicating a phase transition. Below TS, the peaks are well sep-

arated. Similar inference is made for the set of (110) planes.

Even if no clear split is seen in the (112) peak, there is a signif-

icant increase in the calculated FWHM. The values remain

more or less the same till TS. Within the discussed temperature

range below TS, the values increase progressively, showing a

tendency towards a monoclinic distortion. Thus, the tempera-

ture evolution of Bragg peaks indicates the multiple structural

phase transitions occurring in Fe1.12Te. This is significant as

the cross over region in temperature-composition phase dia-

gram shows coexistence of both low temperature crystal struc-

tures (P21/m and Pmmn) as found for lower and higher Fe

content, respectively. The monoclinic distortion is not com-

plete at 36 K from FWHM values. Consequently, we consider

that the low temperature XRD data below TS signals the onset

of a monoclinic distortion.

The lattice parameters and bond angles are plotted as a

function of temperature in Figure 5. The phase transition at

TN is explicitly marked by the drastic change in lattice pa-

rameters. The region above TN is a tetragonal phase while

the shaded regions characterize the temperature range of the

orthorhombic peak broadening. The region below TS is

where the monoclinic distortion is observed. As a conse-

quence of multiple structural phase transition, a single Fe1-

Te distance splits into two at the orthorhombic transition

(TN) and at even lower T, splits into three at the onset

of monoclinic transition (TS). Similar is the case with the

two distinct bond angles of FeTe4 tetrahedra. The

Fe1-Te1-Fe1(1 and 2) bond angles split into two only after

the monoclinic distortion whereas Fe1-Te1-Fe1(3 and 4)

FIG. 3. (a) Splitting of the (101),(�101), and (011) peaks. (b) Splitting of

the (200) and (020) peaks. (c) Peak splitting corresponding to (211),(�211)

and (121), (�121). (d) Peak splitting corresponding to (301) and (031),

(311) and (131), (312), and (�312) and (132). The black lines are the calcu-

lated intensity from refinement. The vertical green lines indicate the possible

Bragg peaks corresponding to the monoclinic (upper row) and orthorhombic

(lower row) space groups for the given 2h range.

FIG. 4. (a) FWHM (with error bars) as a function of temperature. The verti-

cal lines indicate the temperatures at phase transitions as observed in the

thermodynamic data.

123912-3 Cherian et al. J. Appl. Phys. 115, 123912 (2014)

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split at the orthorhombic phase (numbers refer to the inset to

Figure 5(b)). The temperature evolution of bond length and

bond angles gives a vivid picture of the lattice distortion

around the phase transition. The crystal composition investi-

gated here lies near the tricritical point where a mixed mag-

netic phase is predicted.19 The multiple structural transitions

have to be seen in conjunction with the occurrence of mag-

netic phases and its association to different crystal symme-

tries. A detailed study of the magnetic ground states of the

system is relevant as commensurate and incommensurate

AFM ground states are strongly related to the crystal struc-

ture. In a recent study on polycrystalline Fe1þyTe, the transi-

tions are examined as a function of excess Fe(y).17 The

phase diagram provides regions of mixed crystallographic

phases of monoclinic and orthorhombic structure. The com-

position we refer to, falls at the boundary of this mixed phase

region.

Careful estimation and analysis of the unit cell volume

are regarded as crucial in understanding the magneto-elastic

effects. The cell volume in the temperature range from 300 K

to 36 K is estimated from XRD. The unit cell volume in the

high temperature nonmagnetic region is described by a

Gr€uneisen approximation using the Debye equation for the in-

ternal energy, U(T).24 This is expressed as VðTÞ ¼ CUðTÞ=B0 þ V0, where UðTÞ ¼ 9NkBTðT=HDÞ3

ÐHD=T0

x3=ðex� 1Þdx.

C in this context is the Gr€uneisen parameter, B0 is the bulk

modulus, V0 is the zero temperature volume, HD is the Debye

temperature, and N is the number of atoms in the specimen.

The experimental data of the unit cell volume can be

well described by the expression in the nonmagnetic high

temperature region of Figure 6. The fit yields HD

¼ 252:7K; C=B0 ¼ 0:63� 10�10 Pa�1, and V0¼90.73 A3.

However, there are significant deviations at lower tempera-

ture, close to the phase transitions. These deviations become

apparent in the inset to Figure 6 where the high temperature

fit has been extrapolated to below TS. We note that the esti-

mated value of HD will be later compared to a more accurate

value obtained from specific heat data.

Specific heat measurements (Cp) also show two well

separated transitions as already evident in magnetization and

resistivity measurements.19 The second-order lambda-like

transition from paramagnetic to antiferromagnetic phase is

clearly visible at TN¼ 57 K in Figure 7(a). The prominent

peak at 46 K is due to the first-order transition, TS. From syn-

chrotron measurements, we infer that the monoclinic distor-

tion commences at TS. The clear peaks in the specific heat

data corroborate the results of our synchrotron data. The

magnitude of Cp at high temperature falls close to the limit-

ing value given by the Dulong-Petit law, Cp¼ 3rR, where R

is the universal gas constant and r is the number of atoms per

molecule. To evaluate the thermodynamic parameters, the

specific heat is analyzed using the relation Cp ¼ cT þ b1T3

in the ordered region well below the transitions. Figure 7(b)

gives a decent fit in the low temperature region considering

the electronic contribution (linear term) and the phononicFIG. 5. (a) Lattice parameters. (b) Bond angles and (c) bond distances. Bond

distances and bond angles are calculated between the Fe in the square lattice

(Fe1) and Te(Te1). Below TS, the bond angles and bond lengths are calcu-

lated by considering a monoclinic distortion.

FIG. 6. Unit cell volume as a function of temperature. Open circles with the

error bars represent the experimental data and red line represents fit. Inset

gives a magnified low temperature region where the fit deviates.

123912-4 Cherian et al. J. Appl. Phys. 115, 123912 (2014)

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term (T3). HD obtained from the fit is �245.5 K. The HD val-

ues obtained from the specific heat and unit cell volume fit

match very closely. Cp in the nonmagnetic state is modeled

using a combination of Debye and Einstein models25 in the

temperature region 2 K to 300 K using the relation

CðTÞ ¼ cT þ CDebyeðTÞ þ CEinsteinðTÞ;

CDebye ¼ 9rR=x3D

ðxD

0

x4DexD

ðexD � 1Þ2dxD;

CEinstein ¼ 3rRX

i

ai

�x2

EniexEni

ðexEni � 1Þ2�;

(1)

where xD ¼ �hxD=kBT ¼ HD=T and xEni ¼ �hxEni=kBTi

¼ HEni=T. The model is fitted to the data excluding the tran-

sition region from 45 K to 60 K in Figure 7(a). The c and HD

values obtained from the low temperature fit is used for the

entire range. Initially, c is kept fixed to obtain the remaining

parameters. Later, c is varied as a free parameter together

with the other obtained fitting parameters. The lattice terms

with Debye term and two Einstein terms provide the lattice

specific heat. The Sommerfeld coefficient, c obtained from

the fit is 34.1 mJ/mol K2 which is comparable with the previ-

ous reports.3 In Figure 7(c), linear and lattice contributions

are subtracted from the total specific heat to calculate the

excess specific heat Cexe, across the transitions. The first

order transition at TS and the k-like transition at TN are

clearly visible in the Cexe vs T plot. Change in entropy across

the two transitions is obtained from Sexe ¼Ð T

30ðCexe=TÞ dT as

DSexe ¼ 1:3 J=mol K. The change in excess entropy across

the transitions is very small in comparison with Rln2, the

reason for which is attributed to the weak long range mag-

netic ordering.20

Specific heat measurements were also performed at

applied fields 0 T, 5 T, and 9 T across the magnetic and struc-

tural transitions, given in Figure 7(d). The anomaly in Cp

observed at TN does not show any field dependence up to

9 T. On the contrary, TS shifts to lower temperature

ðDT � 1 KÞ, with slight reduction in magnitude of the anom-

aly in Cp. In previous reports, a slight shift is observed in the

coupled magneto-structural transition with applied magnetic

field.26 In our samples, we observe that TS alone shows a

shift in transition temperature. Magnetization data at

1000 Oe in the field cooled warming (FCW) and field cooled

cooling (FCC) protocol and resistivity data are plotted in

Figure 8(a). Magnetization measurements show a similar

trend as observed in polycrystalline sample, with a wide hys-

teresis region.17 Two transition temperatures are pronounced

which are characterized by a sudden drop in magnetization

and resistivity. Temperature derivative of magnetization in

FCC and FCW measurements plotted together in Figure 8(b)

gives a clear picture of the two transitions present. In the de-

rivative plot of magnetization, both TS and TN can well be

identified. On close observation we can see that a hysteresis

starts near 54 K just below TN, where a clear spitting of (200)

diffraction peak occurs due to the orthorhombic structure. The

hysteresis lasts until 30 K, a broad temperature range over

which the first order transition occurs. In the derivative plot of

resistivity (Figure 8(c)), TS clearly stands out as a pronounced

peak whereas TN is seen as a small broad hump.

FIG. 7. (a) Different contributions to specific heat in the temperature range

of 3 K–300 K. (b) Electronic and lattice specific heat fit to the low tempera-

ture Cp. (c) Excess specific heat obtained by subtracting the fit from the total

specific heat. Change in entropy (excess) across the transitions is also plot-

ted. (d) Cp variation in applied magnetic field.

FIG. 8. (a) Magnetization and resistivity plotted as a function of tempera-

ture. (b) Temperature derivative of magnetization in the heating and cooling

measurements showing the two well resolved peaks. A thermal hysteresis

starts below TN where an orthorhombic distortion is observed. (c)

Temperature derivative of resistivity.

123912-5 Cherian et al. J. Appl. Phys. 115, 123912 (2014)

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IV. CONCLUSION

We investigated the structural and magnetic phase tran-

sitions in Fe1.12Te single crystals grown using Bridgman

method. From the synchrotron powder XRD as well as ther-

modynamic and resistivity measurements, the occurrence of

two phase transitions, a magnetic one at TN and a structural

one at TS was confirmed. Upon cooling, the crystal symmetry

of the material is lowered in two steps. Below TN, the crystal

structure adopts an orthorhombic Pmmn symmetry. The

orthorhombic phase partially transforms into a monoclinic

P21/m phase below TS. The present work independently sup-

ports previously published results obtained on polycrystal-

line samples.17 This agreement is remarkable, specifically

when considering the non-stoichiometry of Fe1þyTe and a

random distribution of excess Fe in the lattice. However, a

comparison of the fractions of the Pmmn and P21/m phases

at low temperature may indicate that the single crystals have

a larger volume fraction of the monoclinic phase. The com-

patibility of the commensurate and incommensurate antifer-

romagnetic order associated with the P21/m and Pmmnphases, respectively, is not well understood. The results, in

any case, ascertain the presence of strong magneto-structural

couplings in this system. At present, it is not clear whether

the orthorhombic and monoclinic phases are completely sep-

arated from each other or they rather form an intergrowth.

Consequently, the low-temperature microstructure of

Fe1þyTe appears to be highly complex. A local probe such as

transmission electron microscopy or scanning tunneling mi-

croscopy would be necessary to shed some light on the

microstructural properties of Fe1þyTe at low temperatures.

ACKNOWLEDGMENTS

We acknowledge support by A. Fitch and Y. Watier

at beamline ID31, at ESRF Grenoble, during the experi-

ments based on Proposal No. HS4825. DC thanks S.

Harikrishnan for fruitful discussions. The authors thank

DST (India) and DAAD (Germany) for financial support

and travel grant. The project was partially supported by

DFG SPP 1458. AAT thanks the funding from the ESF

through MTT77.

1S. Margadonna, Y. Takabayashi, M. T. McDonald, K. Kasperkiewicz, Y.

Mizuguchi, Y. Takano, A. N. Fitch, E. Suard, and K. Prassides, Chem.

Commun. 43, 5607 (2008).

2A. Subedi, L. Zhang, D. J. Singh, and M. H. Du, Phys. Rev. B 78, 134514

(2008).3G. F. Chen, Z. G. Chen, J. Dong, W. Z. Hu, G. Li, X. D. Zhang, P. Zheng,

J. L. Luo, and N. L. Wang, Phys. Rev. B 79, 140509 (2009).4B. C. Sales, A. S. Sefat, M. A. McGuire, R. Y. Jin, D. Mandrus, and

Y. Mozharivskyj, Phys. Rev. B 79, 094521 (2009).5S. Li, C. de la Cruz, Q. Huang, Y. Chen, J. W. Lynn, J. Hu, Y. L. Huang,

F. C. Hsu, K. W. Yeh, M. K. Wu, and P. Dai, Phys. Rev. B. 79, 054503

(2009).6F. C. Hsu, J. Y. Luo, K. W. Yeh, T. K. Chen, T. W. Huang, P. M. Wu, Y.

C. Lee, Y. L. Huang, Y. Y. Chu, D. C. Yan, and M. K. Wu, Proc. Natl.

Acad. Sci. U.S.A. 105, 14262 (2008).7K. W. Yeh, T.-W. Huang, Y. L. Huang, T. K. Chen, F.-C. Hsu, P. M. Wu,

Y. C. Lee, Y. Y. Chu, C. L. Chen, J. Y. Luo, D. C. Yan, and M. K. Wu,

Europhys. Lett. 84, 37002 (2008).8Y. Mizuguchi, F. Tomioka, S. Tsuda, T. Yamaguchi, and Y. Takano,

Appl. Phys. Lett. 94, 012503 (2009).9M. H. Fang, H. M. Pham, B. Qian, T. J. Liu, E. K. Vehstedt, Y. Liu, L.

Spinu, and Z. Q. Mao, Phys. Rev. B 78, 224503 (2008).10S. R€oßler, D. Cherian, S. Harikrishnan, H. L. Bhat, S. Elizabeth, J. A.

Mydosh, L. H. Tjeng, F. Steglich, and S. Wirth, Phys. Rev. B 82, 144523

(2010).11B. B€uchner and C. Hess, Nat. Mater. 8, 615 (2009).12F. Ma, W. Ji, J. Hu, Z. Y. Lu, and T. Xiang, Phys. Rev. Lett. 102, 177003

(2009).13Y. Xia, D. Qian, L. Wray, D. Hsieh, G. F. Chen, J. L. Luo, N. L. Wang,

and M. Z. Hasan, Phys. Rev. Lett. 103, 037002 (2009).14W. Bao, Y. Qiu, Q. Huang, M. A. Green, P. Zajdel, M. R. Fitzsimmons,

M. Zhernenkov, S. Chang, M. Fang, B. Qian, E. K. Vehstedt, J. Yang,

H. M. Pham, L. Spinu, and Z. Q. Mao, Phys. Rev. Lett. 102, 247001

(2009).15C. Stock, E. E. Rodriguez, M. A. Green, P. Zavalij, and J. A. Rodriguez-

Rivera, Phys. Rev. B. 84, 045124 (2011).16E. E. Rodriguez, C. Stock, P. Zajdel, K. L. Krycka, C. F. Majkrzak, P.

Zavalij, and M. A. Green, Phys. Rev. B 84, 064403 (2011).17C. Koz, S. R€oßler, A. A. Tsirlin, S. Wirth, and U. Schwarz, Phys. Rev. B

88, 094509 (2013).18E. E. Rodriguez, D. A. Sokolov, C. Stock, M. A. Green, O. Sobolev, J. A.

Rodriguez-Rivera, H. Cao, and A. Daoud-Aladine, Phys. Rev. B 88,

165110 (2013).19S. R€oßler, D. Cherian, W. Lorenz, M. Doerr, C. Koz, C. Curfs, Y. Prots,

U. K. R€oßler, U. Schwarz, S. Elizabeth, and S. Wirth, Phys. Rev. B 84,

174506 (2011).20I. A. Zaliznyak, Z. J. Xu, J. S. Wen, J. M. Tranquada, G. D. Gu, V.

Solovyov, V. N. Glazkov, A. I. Zheludev, V. O. Garlea, and M. B. Stone,

Phys. Rev. B 85, 085105 (2012).21Y. Mizuguchi, K. Hamada, K. Goto, H. Takatsu, H. Kadowaki, and O.

Miura, Solid State Commun. 152, 1047 (2012).22J. R. Carvajal, Physica B 192, 55 (1993).23T. J. Liu, X. Ke, B. Qian, J. Hu, D. Fobes, E. K. Vehstedt, H. Pham, J. H.

Yang, M. H. Fang, L. Spinu, P. Schiffer, Y. Liu, and Z. Q. Mao, Phys.

Rev. B 80, 174509 (2009).24T. Chatterji and T. C. Hansen, J. Phys.: Condens. Matter 23, 276007 (2011).25C. Kant, J. Deisenhofer, A. G€unther, F. Schrettle, A. Loidl, M. Rotter, and

D. Johrendt, Phys. Rev. B 81, 014529 (2010).26R. Hu, E. S. Bozin, J. B. Warren, and C. Petrovic, Phys. Rev. B 80,

214514 (2009).

123912-6 Cherian et al. J. Appl. Phys. 115, 123912 (2014)

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