Influence of oxygen partial pressure on the ferromagnetic properties of polycrystalline Cr-doped ZnO filmsX. Zhang1, W. H. Wang1, L. Y. Li1, Y. H. Cheng1, X. G. Luo1, Hui Liu1, Z. Q. Li2, R. K. Zheng3 and S. P. Ringer3
1 Department of Electronics, Nankai University - Tianjin 300071, PRC
2 Department of Physics, Tianjin University - Tianjin 300072, PRC
3 Australian Key Centre for Microscopy, University of Sydney - New South Wales 2006, Australia
received 21 May 2008; accepted in final form 5 September 2008; published October 2008
published online 6 October 2008
Polycrystalline Cr-doped ZnO films are prepared by the co-sputtering method. Diamagnetism is observed in the conductive samples deposited in pure Ar. However, ferromagnetism is found in films with the same Cr dopant prepared under different oxygen partial pressures. The magnetization shows a strong dependence on the Cr concentration and, especially, on oxygen pressure. It is found that native point defects, which can be adjusted by the oxygen partial pressure during deposition, play a crucial role in the observed magnetic behaviors. The obtained ferromagnetism can be described by the dopant-donor/acceptor hybridization model, which associates exchange interaction with shallow-bound carriers. These results may help to understand the wide range of experimentally determined magnetic moments and its changes with different metal types and concentrations prepared by different groups and methods.
75.50.Pp - Magnetic semiconductors.
75.50.-y - Studies of specific magnetic materials.
75.30.-m - Intrinsic properties of magnetically ordered materials.
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