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Raman studies of ZnO:Co thin films

Huijuan Zhou 1Limei Chen 2Vivek Malik 1,3Christoph Knies 4D,M. Hofmann 4Kanwal P. Bhatti 3Sujeet Chaudhary 3Peter J. Klar 2Wolfram Heimbrodt 2Heinz Kalt 1

1. Universität Karlsruhe (TH), Institut für Angewandte Physik, Wolfgang-Gaede-Str. 1, Karlsruhe 76131, Germany
2. Department of Physics, Renthof 5, Marburg 35302, Germany
3. Indian Institute of Technology Delhi (I.I.T Delhi), hauz Khas, New Delhi, Delhi 110016, India
4. Justus-Liebig-University Giessen, I. Physics Institute, Giessen, Germany

Abstract

Recent theoretical predictions have shown that transition metal doped ZnO can be ferromagnetic with a Curie temperature above room temperature. However experimentally diverse magnetic properties from paramagnetic behavior to ferromagnetism over large temperature range are observed. A common question is whether the magnetic properties are intrinsic, or arise from segregation phases from transition metal clusters.

In this paper we investigate cobalt doped ZnO thin films prepared via sol-gel methods from different groups. Within the concerned doping concentration (0.5%-10%) XRD shows only the diffraction peaks from wurtzite ZnO without secondary phase, as widely reported in literature. Magnetic measurements of the corresponding samples show evidence for ferromagnetic behavior in highly doped samples (> 5%), while normal paramagnetism is found in the lowly doped films. Raman spectroscopy reveals the existence of cobalt oxides like CoO and Co3O4 already in intermediately doped samples. In addition, the Raman shifts of the doped samples exhibit a shift to higher energy with increasing Co doping content. Presently temperature dependent Raman measurements are under way so as to clarify the phase transition of cobalt oxides. The influence of the segregation phases on the magnetic properties of ZnO:Co thin films will be extensively studied.

 

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Related papers

Presentation: Oral at E-MRS Fall Meeting 2006, Symposium E, by Huijuan Zhou
See On-line Journal of E-MRS Fall Meeting 2006

Submitted: 2006-05-15 12:15
Revised:   2009-06-07 00:44