Neutron diffraction and dielectric anomalies in Y Mn 2 − x Fe x O 5Dong Hyun Kim, Sung Baek Kim, and Chul Sung Kim Citation: Journal of Applied Physics 101, 09M104 (2007); doi: 10.1063/1.2711410 View online: http://dx.doi.org/10.1063/1.2711410 View Table of Contents: http://scitation.aip.org/content/aip/journal/jap/101/9?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Crystal structure and magnetic properties of Bi0.8A0.2FeO3 (A = La, Ca, Sr, Ba) multiferroics using neutrondiffraction and Mossbauer spectroscopy AIP Advances 4, 087121 (2014); 10.1063/1.4893241 Disorder-driven spin-reorientation in multiferroic h-YMn1− x Fe x O3 J. Appl. Phys. 116, 024105 (2014); 10.1063/1.4887809 Mössbauer and magnetic studies of multiferroic Mg 0.95 Mn 0.05 Fe 2 − 2 x Ti 2 x O 4 system J. Appl. Phys. 99, 08M910 (2006); 10.1063/1.2172220 Evidence for strong spin-lattice coupling in multiferroic R Mn 2 O 5 ( R = Tb , Dy , Ho ) via thermal expansionanomalies J. Appl. Phys. 99, 08R103 (2006); 10.1063/1.2165586 Structural and magnetic properties of MSr 2 Y 1.5 Ce 0.5 Cu 2 O z (M-1222) compounds with M = Fe and Co J. Appl. Phys. 95, 6690 (2004); 10.1063/1.1688256

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Neutron diffraction and dielectric anomalies in YMn2−xFexO5

Dong Hyun Kim, Sung Baek Kim, and Chul Sung Kima�

Department of Physics, Kookmin University, Seoul 136-702, Korea

�Presented on 11 January 2007; received 7 November 2006; accepted 12 December 2006;published online 2 May 2007�

The multiferroic YMn2−xFexO5 �x=0.00,0.01,0.02,0.04� system has been studied by neutrondiffraction and Mössbauer spectroscopy, focusing on the dielectric constant anomaly near 18 K. Wefound that the electric Curie temperature �TCE� decreased and the second transition anomalytemperature �T2� smeared from the � /�0 curves with higher Fe concentrations in YMn2−xFexO5. Thetemperature dependence of the dielectric constant �� /�0� shows a peak at 41 K and a secondtransition near 18 K for polycrystalline YMn2O5. TCE of YMn1.96Fe0.04O5 was observed at 34 K.The temperature dependence of the lattice parameters for YMn2O5 shows a discontinuous jump at18 K, which is the same anomaly temperature obtained from the dielectric constant curve. TheMössbauer electric quadrupole splitting value also changed at 21 K for YMn1.99Fe0.01O5. Our dataindicate that the changes in the lattice and Mössbauer parameters occur simultaneously with theanomaly of dielectric constant. © 2007 American Institute of Physics. �DOI: 10.1063/1.2711410�

I. INTRODUCTION

Multiferroic materials are systems where the electric andmagnetic properties are coupled together.1 In these materials,the magnetization is induced by the electric field or the spon-taneous polarization is induced by the magnetic field. Con-sequently, there are interactions of ferroelectric and magneticproperties. Recently, numerous researches have been focusedon the multiferroic RMn2O5 �R=rare earth� materials2–4 andit is shown that the dielectric anomaly in RMn2O5 is due tothe lattice effect.5 These materials possess ferroelectric prop-erties and antiferromagnetic property disappears in the lowtemperature region. Especially, the single crystal of YMn2O5

materials show dielectric constant anomalies at 19 and39 K.6

In this paper, we have studied the magnetic and electricproperties of YMn2O5 with nonmagnetic Y3+ ion by dielec-tric constant, neutron diffraction, and Mössbauer spectros-copy measurement.

II. EXPERIMENT

Polycrystalline YMn2O5 was obtained by the sol-gelprocess.7 Starting materials were yttrium�II� nitrate hexahy-drate �Y�NO3�2 ·6H2O� and manganese�II� acetate tetrahy-drate �Mn�CH3CO2�2 ·4H2O�. These were dissolved andmixed in a solvent system �ethanol: acetic acid:2-methoxyethanol: distilled water: ethylene glycol=10:4 :4 :1 :1 ratio�. The solution was refluxed at 80 °C for18 h and dried at 120 °C. Afterwards, the dried mixtureswere calcined at 400 °C for 3 h. The samples were crystal-lized at 1100 °C for 6 h in O2 gas balance.

The crystalline structure was analyzed using PhilipsX’Pert diffractometer with Cu K� radiation source. The di-electric constant was measured by physical properties mea-surement system �PPMS�. Neutron diffraction data were in-

vestigated using the high-resolution powder diffractometer atthe Korea Atomic Energy Research Institute Reactor HA-NARO. Neutrons with wavelength of 1.835 Å were obtainedby �331� reflection of Ge monochromator in the temperaturerange from 4.2 K to room temperature. Mössbauer spectrawere also taken in the temperature range from 4.2 K to roomtemperature using conventional transmission geometry witha 57Co �-ray source �50 mCi� in Rh matrix.8

III. RESULTS AND DISCUSSION

Figures 1�a� and 1�b� show the x-ray diffraction �XRD�and neutron diffraction patterns of polycrystalline YMn2O5

at room temperature, respectively. The diffraction patternswere refined by Rietveld profile analysis using the FULLPROF

a�Author to whom correspondence should be addressed; FAX: 82-2-910-5170; electronic mail: cskim@phsy.kookmin.ac.kr

FIG. 1. �a� X-ray and �b� neutron diffraction patterns of YMn2O5 at roomtemperature. Solid circle represents the observed pattern; continuous linesrepresent the calculated and difference �obs.−calc.� patterns. Tick markerscorrespond to the position of the allowed Bragg reflections.

JOURNAL OF APPLIED PHYSICS 101, 09M104 �2007�

0021-8979/2007/101�9�/09M104/3/$23.00 © 2007 American Institute of Physics101, 09M104-1

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program. The crystalline structure of YMn2O5 was found tobe orthorhombic �Pbam� at room temperature. The Mn3+

ions are base centered of oxygen square pyramidal and theMn4+ ions are centered of oxygen octahedral.9 The latticeparameters of YMn2O5 were determined to be a0=7.275 Å,b0=8.487 Å, and c0=5.674 Å with an orthorhombic �Pbam�structure. The Bragg factors RB and RF were 3.14% and3.30%, respectively.

Figure 2 shows the temperature dependence of the di-electric constant for YMn2−xFexO5 �x=0,0.01,0.02,0.04�powders. Even though the samples were polycrystals, thedistinct dielectric constants were well behaved and changednear the magnetic Néel temperature �TN� and the electricCurie temperature �TCE� shown in Table I. Also, with in-creasing Fe concentrations of the YMn2−xFexO5, the TCE

decreased and the second transition anomaly temperature�T2� smeared in the � /�0 curves. Particularly, we focus onthe dielectric constant near the second transition anomalytemperature �T2�. In a previous report,6 it was observed thatthe susceptibility and the permittivity changed together atT2 as shown in Fig. 2. However, the origin of the simulta-

neous occurrence is not well understood. In order to clarifythis, we have obtained neutron diffraction data at varioustemperatures.

The neutron diffraction was taken at 4 K and then ob-tained from 15 to 23 K in 2 K intervals. The changes in lat-tice parameters of YMn2O5 are shown in Fig. 3. The latticeparameters do not change until 15 K; however, a0 and b0

decrease rapidly near 18 K, while c0 increases smoothly. Wenote that this temperature is identical to the temperature �T2�of the dielectric constant anomaly of YMn2O5 in Fig. 2�a�.Our neutron diffraction results suggest that the importantchanges of crystal lattice parameters, bond lengths, andangles occur in this region ��T2�. These changes may affect

FIG. 4. Mössbauer spectra of YMn1.99Fe0.01O5 at various temperatures.

FIG. 2. Dielectric constant of YMn2−xFexO5 from 10 to 80 K: �a� x=0, �b�x=0.01, �c� x=0.02, and �d� x=0.04.

TABLE I. Dielectric constant second transition anomaly temperature �T2�,electric Curie temperature �TCE�, and magnetic Néel temperature �TN� ofYMn2−xFexO5 at various temperatures.

X T2 TCE TN

0 18 41 450.01 21 39 470.02 23 36 490.04 ¯ 34 50

FIG. 3. Lattice parameters of YMn2O5 at various temperatures by neutrondiffraction analysis.

09M104-2 Kim, Kim, and Kim J. Appl. Phys. 101, 09M104 �2007�

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the microscopic local structure of charge distribution andthen one may get a large electric quadrupole anomaly nearT2.

In order to obtain the microscopic electric and magneticinteraction mechanism, we have obtained Mössbauer spectraat various temperatures. Figure 4 shows the Mössbauer spec-tra of YMn1.99Fe0.01O5 at various temperatures ranging from4.2 to 47 K. The magnetic Néel temperature �TN� was deter-mined to be 47 K. The Mössbauer spectra below TN exhibitsix-line two-set patterns, but they coalesce into two linesabove TN. A variation of the electric quadrupole splitting forthe YMn1.99Fe0.01O5 appeared at 21 K, as shown in Fig. 5.This temperature is identical to the second transitionanomaly temperature �T2� of the dielectric constant curve inFig. 2. The electric quadrupole splitting values at 4.2 K are0.35 and −0.09 mm/s on A and B sites, respectively. In thecrystal symmetry of Pbam, Mn3+ and Mn4+ are at pyramidal

and octahedral sites, respectively. The pyramidal site haslower crystal symmetry than the octahedral site. Thereforeone may get a larger electric quadrupole splitting in the py-ramidal site than in the octahedral site. Finally, we concludethat the Mössbauer spectra of the Fe ions for the A and Bsites correspond to the Mn3+ and the Mn4+, respectively.

In summary, the distinct dielectric constants were ob-served in YMn1.99Fe0.01O5. We have observed that changesin the lattice parameters and electric quadrupole splitting oc-curred at the dielectric constant second transition anomalytemperature �T2� by neutron diffraction and Mössbauer spec-troscopy analysis with Fe3+ ions occupying the Mn3+ and theMn4+ site.

ACKNOWLEDGMENTS

This work was supported by the Korea Research Foun-dation Grant No. KRF-2005-070-C00050.

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FIG. 5. Temperature dependence of electric quadrupole splitting forYMn1.99Fe0.01O5: �a� pyramidal site and �b� octahedral site.

09M104-3 Kim, Kim, and Kim J. Appl. Phys. 101, 09M104 �2007�

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