Room-temperature ferromagnetism of Cu ion-implanted Ga-doped ZnO

1 MeV Cu ² ions have been implanted into un-doped ZnO and Ga-doped ZnO films with a dose of 1 × 10 ¹⁷ ions/cm ² at room-temperature. Cu ion-implanted Ga-doped ZnO had ferromagnetism at room-temperature and the saturation magnetization of this sample was estimated to be 0.12 μ _B per Cu, while the Cu ion-implanted un-doped ZnO did not show ferromagnetic behavior. Near-edge X-ray fine structure (NEXAFS) spectroscopy revealed that a partial amount of implanted Cu ions existed as Cu ² (d ⁹) state in Ga-doped ZnO film. On the other hand, almost Cu atoms existed as Cu ¹ (d ¹⁰) state in un-doped ZnO film. However, the subsequent annealing at temperature above 800°C on this ferromagnetic sample induced the annihilation of ferromagnetism due to the formation of non-ferromagnetic Cu ₂O phase.