Interpretation of ferromagnetic Fe doped ZnO by Mössbauer spectroscopySeung-Iel Park, Geun Young Ahn, and Chul Sung Kim Citation: Journal of Applied Physics 101, 09H113 (2007); doi: 10.1063/1.2712527 View online: http://dx.doi.org/10.1063/1.2712527 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 Magnetic properties of Fe doped, Co doped, and Fe+Co co-doped ZnO J. Appl. Phys. 113, 17C308 (2013); 10.1063/1.4799778 Photoluminescence studies on structural defects and room temperature ferromagnetism in Ni and Ni–H dopedZnO nanoparticles J. Appl. Phys. 108, 023906 (2010); 10.1063/1.3460644 Role of point defects in room-temperature ferromagnetism of Cr-doped ZnO Appl. Phys. Lett. 91, 072511 (2007); 10.1063/1.2772176 Effects of hydrogenated annealing on structural defects, conductivity, and magnetic properties of V-doped ZnOpowders Appl. Phys. Lett. 90, 222505 (2007); 10.1063/1.2745642 Magnetic properties of hydrogenated Li and Co doped ZnO nanoparticles Appl. Phys. Lett. 89, 202507 (2006); 10.1063/1.2387877

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Interpretation of ferromagnetic Fe doped ZnO by Mössbauer spectroscopySeung-Iel Park, Geun Young Ahn,a� and Chul Sung Kimb�

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

�Presented on 11 January 2007; received 31 October 2006; accepted 23 December 2006;published online 3 May 2007�

Single phase Zn0.95Fe0.05O sample was obtained by the sol-gel method with annealing at 650 °C for6 h in H2 5%/Ar balance gas atmosphere. The crystalline structure of Zn0.95Fe0.05O is determined tobe a P63mc hexagonal structure with lattice constants a0=3.255 Å and c0=5.207 Å at roomtemperature. The Mössbauer spectra were obtained at various temperatures ranging from4.2 to 295 K. The values of the isomer shifts ��� show that for all temperature ranges, they are inthe ferrous �Fe2+� state. The magnetic hyperfine field �Hhf� and electric quadrupole splitting ��EQ�in the weak ferromagnetic state at 4.2 K have been analyzed, yielding the following results: Hhf

=37.8 kOe, �=67.5°, �=0°, �=0.75, �EQ=2.06 mm/s, and R=7.4, respectively. From theMössbauer spectrum at 77 K, the paramagnetic quadrupole phase is related to the temperaturedependence of spin-lattice relaxation. © 2007 American Institute of Physics.�DOI: 10.1063/1.2712527�

I. INTRODUCTION

Transition metal �Fe, Co, Ni, etc.� doped ZnO based di-luted magnetic semiconductors have been studied by manyresearchers since Dietl et al.1 demonstrated ferromagneticproperties at room temperature by dilute doping with a tran-sition metal. Recently, the ferromagnetic properties for theZnO based magnetic semiconductor at room temperature waselucidated to occur with the oxygen defects in zinc oxide andits various charge states are due to the covalent oxygen-oxygen bond.2,3 Also, researches on TiO2 based magneticsemiconductor have taken this influence into consideration.4

In this paper, we present the results of Mössbauer experi-ments for the 57Fe doped ZnO sample which were analyzedwith the consideration of Hhf, �e2qQ, �, �, and � and com-pare them with those of the x-ray diffraction analysis.

II. EXPERIMENT

Single phase polycrystalline Zn0.9557Fe0.05O was ob-

tained by the sol-gel method5 with annealing in hydrogen/argon. The crystalline structure of the sample was analyzedby the long time scanning of 2 h using a Philips x-ray dif-fractometer with Cu K� radiation. For the analysis with thehyperfine magnetic property, Mössbauer spectra were mea-sured at various temperatures ranging from 4.2 to 295 K.

III. RESULTS AND DISCUSSION

Figure 1 shows the x-ray diffraction patterns of theZn0.95

57Fe0.05O at room temperature by Rietveld refinementanalysis. The crystalline structure of Zn0.95

57Fe0.05O was de-termined to be a wurtzite hexagonal symmetry of P63mcwith lattice constants a0=3.255 Å and c0=5.207 Å at roomtemperature, while the Bragg RB and Rf factors were 2.60%and 2.05%, respectively. The composition of 57Fe doped

ZnO sample was determined to be Zn0.9557Fe0.05O1.21 by

x-ray diffraction analysis. These defects in the Fe doped ZnOsample are due to the annealing condition in the H2 5%/Arbalance gas atmosphere. With the x-ray analysis results, weconsidered a highly symmetric state for interstitial oxygen,which is identical to the investigation of Erhart et al.3 andZhang co-workers.6,7 This phenomenon is responsible for theferromagnetic interaction in the ZnO structure.

Figure 2 shows the applied field dependence of the mag-netic curve at 60 K and room temperature. For the substitu-tion of isotope 57Fe, the ferromagnetic property appeared tobe smaller when compared with the natural Fe substituted.4

However, as shown in Fig. 2, a shape of very weak ferro-magnetic behavior is shown at room temperature. This resultwas explained with a highly symmetric state for interstitial

a�Present address: Department of Neutron Physics, HANARO, KAERI,Yuseong, Daejeon 305-600, Korea.

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

FIG. 1. The x-ray diffraction pattern of the Zn0.9557Fe0.05O at room tem-

perature. The open circles represent the observed patterns; continuous linesrepresent calculated and difference �obs-cal� patterns. The tick marks corre-spond to the position of the allowed Bragg reflections.

JOURNAL OF APPLIED PHYSICS 101, 09H113 �2007�

0021-8979/2007/101�9�/09H113/3/$23.00 © 2007 American Institute of Physics101, 09H113-1

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oxygen from the defect in 57Fe doped ZnO structure. Also,this very weak ferromagnetic behavior was due to the weakinteraction between Fe2+ ions and the oxygen occupancy ra-tio in the ZnO lattice.5

In order to study ferromagnetic properties with thishighly symmetric state, Mössbauer spectra of the samplewere measured at various absorber temperatures from4.2 to 295 K. Mössbauer spectra were analyzed using theeight Lorentzian fittings, which are described in detail in

Ref. 8, as shown in Fig. 3. The magnetic hyperfine field andthe electric quadrupole splitting in the weak ferromagneticstate at 4.2 K have been analyzed, yielding the followingresults: Hhf=37.8 kOe, �=67.5°, �=0°, �=0.75,�EQ=2.06 mm/s, and R=7.4, respectively. From the Möss-bauer spectrum at 77 K, the paramagnetic quadrupole phase�dotted line in Fig. 3� appears due to the temperature depen-dence of spin-lattice relaxation. As the temperature increases,the paramagnetic quadrupole phase increases though theweak ferromagnetic phase remains at 295 K.

Figures 4�a� and 4�b� show the temperature dependenceof the magnetic hyperfine field and the quadrupole splittingand isomer shift for the Zn0.95

57Fe0.05O. The values of theisomer shifts show that for all the temperature ranges, thephases are in the ferrous �Fe2+� state, which is relative to�-Fe metal at room temperature. Also, the paramagneticquadrupole phase above 77 K has the ferrous state value. Atthe low temperature ranges, the quadrupole splittings havelarge values, but they rapidly decrease with increasing tem-perature. It is notable that as the temperature decreases below295 K, quadrupole splitting increases, which suggests thepresence of an electric field gradient and accompanying spin-lattice relaxation effects. Namely, the ferromagnetic revela-tion of Zn0.95

57Fe0.05O was due to the temperature depen-dence of the quadrupole splitting and the spin-latticerelaxation by the crystalline defects and diluted doping.

In conclusion, we suggest that the ferromagnetic proper-FIG. 3. The Mössbauer spectra for Zn0.9557Fe0.05O at various temperatures.

FIG. 4. The temperature dependence of the magnetic hyperfine fields �a� andthe quadrupole splitting and isomer shift �b� for the Zn0.95

57Fe0.05O.

FIG. 2. The applied field dependence of the magnetization curve per unitmolecule for Zn0.95

57Fe0.05O at 60 K and room temperature.

09H113-2 Park, Ahn, and Kim J. Appl. Phys. 101, 09H113 �2007�

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ties in Zn0.9557Fe0.05O are due to the covalent oxygen-

oxygen bond interaction by the highly symmetric state forinterstitial oxygen and the weak interaction between themagnetic ions and the oxygen occupancy ratio in ZnOlattice.3,5–7 This leads to a change in the shape of crystalfields of 57Fe ion in ZnO sample by electric distribution andmagnetic interaction.

ACKNOWLEDGMENTS

This research was supported by the Research Center forAdvanced Magnetic Materials �KOSEF� at ChungnamUniversity.

1T. Dietl, H. Ohno, F. Matsukura, J. Cibert, and D. Ferrand, Science 287,1019 �2000�.

2M. H. F. Sluiter, Y. Kawazoe, P. Sharma, A. Inoue, A. R. Raju, C. Rout,and U. V. Waghmare, Phys. Rev. Lett. 94, 187204 �2005�.

3P. Erhart, A. Klein, and K. Albe, Phys. Rev. B 72, 085213 �2005�.4K. J. Kim, Y. R. Park, G. Y. Ahn, and C. S. Kim, J. Magnetics �Seoul� 11,12 �2006�.

5G. Y. Ahn, S.-I. Park, S. J. Kim, B. W. Lee, and C. S. Kim, IEEE Trans.Magn. 41, 2730 �2005�.

6S. B. Zhang, S.-H. Wei, and A. Zunger, Phys. Rev. B 63, 075205 �2001�.7S. Limpijumnong, S. B. Zhang, S.-H. Wei, and C. H. Park, Phys. Rev.Lett. 92, 155504 �2004�.

8J. Y. Park, H. M. Ko, W. H. Lee, S. H. Ji, and C. S. Kim, J. Appl. Phys. 73,5707 �1993�.

09H113-3 Park, Ahn, and Kim J. Appl. Phys. 101, 09H113 �2007�

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