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The Er ions have been introduced into ZnO films prepared by radio-frequency magnetic sputtering (RFMS) on sapphire substrates by ion implantation. The annealing effect on structural and magnetic properties for Er-implanted ZnO films under air, Ar, and vacuum atmospheres at 650 °C have been investigated systematically by a combined characterization of X-ray diffractions, Raman spectroscopy, Photoluminescence, X-ray photoelectron spectroscopy and Superconducting Quantum Interference Device. Strong room-temperature ferromagnetism has been observed for the as-implanted and annealed films. We found that the saturation magnetization varied greatly for different annealing conditions. A considerable enhancement in magnetization is observed for Er-doped ZnO annealed in vacuum, which is accompanied by an enhancement in the concentration of oxygen vacancy. Our results give clear evidence that the enhancement of ferromagnetism is strongly correlated with the increase of oxygen vacancies in Er-doped ZnO.

Different concentrations of arsenic ions have been introduced into high quality O polar ZnO films prepared by rf-plasma assisted molecular beam epitaxy on sapphire substrates by ion implantation. Rutherford Backscattering/Channeling, x-ray diffraction, Raman spectroscopy and optical absorption measurements have been carried out to characterize the implantation induced disorder in the ZnO films. Room temperature ferromagnetism has been observed for the films implanted with As dose higher than 6×10 18 cm −3 . The size of the observed moment is too large to be attributed to the As related defect complex (As Zn -2V Zn ) and is attributed to defects introduced by the ion implantation process. This was confirmed by the observation that the magnetization could be removed by annealing the films.

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.