Influence of oxygen partial pressure on the ferromagnetic properties of polycrystalline Cr-doped ZnO films

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

Corresponding author: liuhui@nankai.edu.cn

Received: 21 May 2008
Accepted: 5 September 2008

Abstract

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.