Oxygen enhanced ferromagnetism in Cr-doped ZnO films

Cr-doped ZnO films have been prepared by inductively coupled plasma enhanced physical vapor deposition, and an in-depth study is performed on the chromium doping and oxygen partial pressure dependence of ferromagnetism. The x-ray diffraction and photoluminescence results indicate that the moderate oxygen can relax the lattice strain thus enhancing ferromagnetism which, as confirmed by soft x-ray absorption spectroscopy, is mainly attributed to the Cr valence state transition from Cr3+ to Cr6+. However, excessive oxygen suppresses the oxygen vacancies and the ferromagnetic exchange. Furthermore, the parabola-like dependence of ferromagnetism on oxygen partial pressure is consistent with the bound magnetic polaron scenario. (C) 2011 American Institute of Physics. [doi:10.1063/1.3624589]