Raman spectroscopy and magnetic properties of bulk Zn0984Co0.016O crystal

Wojciech Szuszkiewicz 1Jean-Francois Morhange 2Andrzej Lusakowski 1Zbigniew Golacki 1Monika Arciszewska 1Beata B. Brodowska 1Marcin Klepka 1Witold Dobrowolski 1

1. Polish Academy of Sciences, Institute of Physics, al. Lotników 32/46, Warszawa 02-668, Poland
2. Institut des nanosciences de Paris (INSP), 140 rue de Lourmel, Paris 75015, France

Abstract

An analysis of the structural and magnetic properties of bulk Zn0984Co0.016O mixed crystal have been performed using Raman scattering and magnetization measurements. The exact Co content in crystals grown by chemical vapour transport was determined using an electron microprobe. The optical measurements were performed at several temperatures between 15 K and 295 K, the magnetic properties were investigated in a wide temperature range from 5 K to 295 K.

Beside the phonons characteristic for the ZnO host lattice, in the Raman spectra we observed a disorder-induced lattice vibration modes and a structure which was assigned to a local vibration mode of the Co impurity. Moreover, in the Raman spectra we also observed lines resulting from light scattering on phonons in hcp-Co and on magnons in CoO.  This may be considered as an experimental confirmation of the presence of such precipitates in the investigated sample. The temperature dependence of the Raman spectra confirms this interpretation.

Apart from the high frequency structures mentioned above, we observed also two lines in the low frequency region (at 5 cm-1 and at 13 cm-1). The first line may be ascribed to the splitting of the ground state of Co2+ ion in the crystal field of wurtzite symmetry. The second line may be due to the ground state splitting of Co2+ ion in CoO. Some other explanations, like possible presence of other precipitates (ZnCo2O4) or local deformation of Co2+ ion neighborhood are also analyzed and discussed.

Finally,  we discuss an influence of precipitates on the magnetization of the sample.

 

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Presentation: Oral at E-MRS Fall Meeting 2008, Symposium A, by Wojciech Szuszkiewicz
See On-line Journal of E-MRS Fall Meeting 2008

Submitted: 2008-05-12 23:39
Revised:   2009-06-07 00:48