Surface-polarity-dependent ferromagnetism in arsenic-implanted ZnO films prepared by MBE

Abstract O-polar and Zn-polar ZnO films were prepared by rf-plasma assisted molecular beam epitaxy (MBE) on sapphire substrates. Arsenic ions have been implanted into high quality ZnO with a definite polarity. Substantial temperature-independent ferromagnetism has been observed for both films, with the O-polar film having approximately twice the magnetization as the Zn-polar film. The saturation magnetization is shown to be due to the defects introduced during implantation, rather than to local moments associated with the As ion. Rutherford Backscattering/Channeling and optical absorption measurements confirm that the implantation introduces more defect states in the O-polar films, while X-ray absorption near-edge structure measurements show that the environment of the arsenic ions was similar for both polarities.