Exceptional magnetic properties of Fe substituted nickel chromiteSeung-Iel Park and Chul Sung Kim Citation: Journal of Applied Physics 101, 09N511 (2007); doi: 10.1063/1.2712325 View online: http://dx.doi.org/10.1063/1.2712325 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 Effect of Ni substitution on Y-type barium ferrite J. Appl. Phys. 113, 17D906 (2013); 10.1063/1.4794879 Sintering effect on structural and magnetic properties of Ni 0.6 Zn 0.4 Fe 2 O 4 ferrite AIP Conf. Proc. 1512, 1160 (2013); 10.1063/1.4791460 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 Magnetic property and charge ordering effect in polycrystalline Lu Fe 2 O 4 J. Appl. Phys. 103, 07E307 (2008); 10.1063/1.2838999 Magnetic and structural properties of ultrafine Ni–Zn–Cu ferrite grown by a sol–gel method J. Appl. Phys. 87, 6241 (2000); 10.1063/1.372667

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Exceptional magnetic properties of Fe substituted nickel chromiteSeung-Iel Park and Chul Sung Kima�

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

�Presented on 11 January 2007; received 7 November 2006; accepted 21 December 2007;published online 3 May 2007�

The NiCr2−xFexO4, �x=0.1,0.3,0.5� samples have a cubic structure at room temperature. For thesample with x=0.1, the lattice constant is determined to be a0=8.319 Å with a cubic spinel �Fd-3m�structure. The ferrimagnetic Néel temperature �TN� of NiCr2O4 is determined to be 80 K by zerofield cooled magnetization curves under the external field of 100 Oe. With increasing Fesubstitution, TN increases, and for x=0.1, TN is determined to be 135 K. For the sample with x=0.1, the Mössbauer spectrum at 4.2 K was fitted to two magnetic components of the magnetichyperfine fields Hhf=488 and 472 kOe and isomer shifts �=0.29 and 0.28 mm/s. The electricquadrupole splittings ��EQ� were found to be nearly zero below the TN=135 K. For the spectrumat 295 K, the �EQ are observed with large values of 0.54 and 0.37 mm/s, respectively. The valuesof the isomer shifts show that for all temperature ranges, the states are ferric �Fe3+�. The Mössbauerspectra below the TN show the line broadening with the Jahn-Teller distortion and accompanyingrelaxation effects, respectively. © 2007 American Institute of Physics. �DOI: 10.1063/1.2712325�

I. INTRODUCTION

Recently, many researchers have been interested in theproperties of chromite �ACr2O4; A=Co,Ni, etc.� for spinelstructure material with multiferroic effects.1,2 The NiCr2O4 isa ferrimagnet cubic normal spinel above 302 K, in whichNi2+ ions occupy the tetrahedral sites and Cr3+ ions occupythe octahedral sites. Also in the NiCr2−xFexO4 system, thereis a cubic to tetragonal �c /a�1� transition for the Fe con-centration x�0.2 under room temperature.3

In this paper we have studied the Ni chromite NiCr2O4

with Fe doping, and evaluated the impact on magnetic prop-erties by x-ray diffraction, magnetization, and Mössbauerspectroscopy measurements.

II. EXPERIMENT

Polycrystalline samples of the NiCr2−xFexO4 �x=0.0,0.1,0.3,0.5� were prepared with the sol-gel method.The ultimate single phase samples were obtained by anneal-ing for 12 h in atmosphere at 1000 °C. The crystal structurewas analyzed using a Philips x-ray diffractometer withCu K� radiation. Magnetization curves were also obtainedwith a vibrating sample magnetometer �VSM�. The hyperfinemagnetic property of samples was measured by using Möss-bauer spectroscopy.

III. RESULT AND DISCUSSION

The crystalline structure of NiCr2O4 was determined tobe a tetragonal symmetry of I41amd with lattice constantsa0=5.838 Å and c0=8.437 Å at 295 K by Rietveld refine-ment, while the Bragg RB and RF factors were 4.44% and3.93%. The Fe substituted NiCr2−xFexO4 �x=0.1,0.3,0.5�samples at room temperature revealed a cubic spinel symme-

try of Fd-3m as shown in Fig. 1. However, the Fe substitutedsamples have a cubic to tetragonal transition under roomtemperature.3 For NiCr1.9Fe0.1O4, the lattice constant wasa0=8.319 Å, which was obtained by Rietveld refinement,while the RB and RF were 2.56% and 2.36%, respectively.For the Fe substituted samples, the lattice constants decreasewith increasing Fe substitution, as listed in Table I andshown in Fig. 2�a�.

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

FIG. 1. The x-ray diffraction patterns of NiCr2−xFexO4 �x=0.0,0.1,0.3,0.5� at room temperature. The open circles represent the ob-served patterns; continuous lines represent calculated and difference �obs-cal� patterns. The tick marks correspond to the position of the allowed Braggreflections.

JOURNAL OF APPLIED PHYSICS 101, 09N511 �2007�

0021-8979/2007/101�9�/09N511/3/$23.00 © 2007 American Institute of Physics101, 09N511-1

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Figure 2�a� shows the Fe substitution �x� dependence ofthe ferrimagnetic Néel temperature �TN�. The TN is deter-mined by comparing the d� /dT curve of the zero fieldcooled �ZFC� results with the Mössbauer spectra analysis.Increasing of the Fe substitution increased TN, as listed inTable I. Figure 2�b� shows the temperature dependence of theZFC magnetization curves for the NiCr2−xFexO4 �x=0.0,0.1,0.3,0.5� under a low external field of 100 Oe. Themagnetic Néel temperature of the NiCr2O4 is determined tobe 80 K by the d� /dT curve of the ZFC, as shown in the

inner box in Fig. 2�b�. This result is identical to the reportedvalue of Love and Obenshain.4 The different shapes of theZFC magnetization curves in Fig. 2 were due to the crystal-line properties objected by the quantity of the substituted Feion.3 For the sample x=0.1, the Néel temperature is deter-mined to be TN=135 K.

Figure 3 shows the Mössbauer spectra of NiCr2−xFexO4

�x=0.1,0.3,0.5� at room temperature. Mössbauer spectra ofthe Fe substituted NiCr2−xFexO4 �x=0.1,0.3,0.5� were mea-sured at various temperatures ranging from 4.2 to 295 K.The Mössbauer spectra of all samples indicate that there aretwo magnetic phases, which are due to the two different sitesof the Cr3+ state.1 The Mössbauer spectrum of the Fe substi-tuted nickel chromites at 4.2 K was different in its shapewhen compared with Ni-site absorption lines for NiCr2O4.5

Also, the magnetic hyperfine fields have different valuesfrom those of an inverse spinel Ni ferrite.6 Namely, the sub-stituted Fe ions make a uniform substitution with two differ-ent sites of Cr3+ by sol-gel growth method. The Mössbauerspectrum of the x=0.5 sample shows the resonance absorp-

TABLE I. The lattice constants a0 and c0, unit cell volume V, magnetic Néel temperature TN, the magnetic hyperfine fields Hhf, the electric quadrupolesplittings �EQ, and the isomer shifts � for NiCr2−xFexO4 �x=0.0,0.1,0.3,0.5� at room temperature.

x ao �� co ��V

�Å3�TN

�K�

Hhf �kOe� �EQ �mm/s� � �mm/s� Area �%�

a b a b a b a b

0.0 5.846 8.413 574.83 80 ¯ ¯ ¯ ¯ ¯ ¯ ¯ ¯

0.1 8.319 ¯ 575.72 135 ¯ ¯ 0.46 0.45 0.105 0.199 50.4 49.60.3 8.317 ¯ 575.30 230 ¯ ¯ 0.49 0.50 0.101 0.209 50.2 49.80.5 8.312 ¯ 574.27 375 357 316 0.01 −0.01 0.156 0.158 50.6 49.4

Deviation ±0.001 ±0.001 ±0.01 ±2 ±5 ±5 ±0.01 ±0.01 ±0.001 ±0.001 ±0.5 ±0.5

FIG. 2. �a� The ferrimagnetic Néel temperature �TN� and lattice constant atroom temperture and �b� the temperature dependence of the zero field cooled�ZFC� magnetization curves for NiCr2−xFexO4 �x=0.0,0.1,0.3,0.5� underthe external field of 100 Oe. The inner box is d� /dT curve of x=0.0 sample,with the arrow indicating the TN point.

FIG. 3. The Mössbauer spectra of NiCr2−xFexO4 �x=0.1,0.3, 0.5� at roomtemperature.

09N511-2 S.-I. Park and C. S. Kim J. Appl. Phys. 101, 09N511 �2007�

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tion shape of the two-site sextet at room temperature, belowthe Néel temperature. This is indicated in Table I.

Figure 4 shows the Mössbauer spectra for theNiCr1.9Fe0.1O4 at various temperatures. For the sample withx=0.1, the spectrum at 4.2 K was fitted to two magneticcomponents of the magnetic hyperfine fields Hhf=488 and472 kOe and isomer shifts �=0.29 and 0.28 mm/s, respec-tively. The average value curve for the temperature depen-dence of the magnetic hyperfine fields agrees with the spin

1/2 curve obtained by the Brillouin function with molecularfield theory. The electric quadrupole splittings ��EQ� werefound to be nearly zero below the TN=135 K. For the spec-trum at 295 K, the �EQ are observed with large values of0.54 and 0.37 mm/s, respectively. The values of the isomershifts show that at all temperature ranges, the states are ferric�Fe3+�, which is relative to �-Fe metal at room temperature.The Mössbauer spectra below the TN show the line broaden-ing with the Jahn-Teller distortion and accompanying relax-ation effects as shown in Fig. 4. The line broadening withincreasing temperature originates from different temperaturedependencies of the magnetic hyperfine fields at various ionsites as determined using the molecular field theory.7

In summary, we have studied with Mössbauer spectros-copy the Fe doped NiCr2−xFexO4 �x=0.0,0.1,0.3,0.5�. TheJahn-Teller distortion due to the crystalline phasetransition3,8 and accompanying relaxation effects in the Fedoped nickel chromites were identified by Mössbauer spec-troscopy analysis to be temperature dependent.

ACKNOWLEDGMENTS

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

1K. Tomiyasu, J. Fukunga, and H. Suzuki, Phys. Rev. B 70, 214434 �2004�.2L. G. Antoshina, A. N. Goryaga, and D. A. Chursin, Phys. Solid State 44,747 �2002�.

3R. J. Arnott, A. Wold, and D. B. Rogers, J. Phys. Chem. Solids 25, 161�1964�.

4J. C. Love and F. E. Obenshain, AIP Conf. Proc. 18, 513 �1974�.5J. Göring, W. Wurtinger, and R. Link, J. Appl. Phys. 49, 269 �1978�.6S. W. Lee and C. S. Kim, J. Magnetics �Seoul� 10, 5 �2005�.7C. S. Kim, H. M. Ko, W. H. Lee, and C. S. Lee, J. Appl. Phys. 73, 6298�1993�.

8J. Kanamori, M. Kataoka, and Y. Iroh, J. Appl. Phys. 39, 688 �1968�.

FIG. 4. The Mössbauer spectra at various temperatures for NiCr1.9Fe0.1O4.

09N511-3 S.-I. Park and C. S. Kim J. Appl. Phys. 101, 09N511 �2007�

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