Effect of substrate temperature on the room-temperature ferromagnetism of Cu-doped ZnO films

Wurtzite structure ZnO films doped with ~2 at% Cu were deposited at substrate temperatures (Ts) from 350 to 600 °C by helicon magnetron sputtering. All the films exhibited room-temperature (RT) ferromagnetism (FM) and the maximum saturation magnetization (Ms) was 1.2 emu/cm3 (~0.15 μB/Cu). Cu ions were mainly in a divalent state as identified by X-ray photoelectron spectroscopy. FM tended to increase with decreasing Ts, and vacuum annealing enhanced the Ms. These results suggested that oxygen vacancies and/or zinc interstitials might contribute to the ferromagnetic performance. Thus, the observed FM was explained in terms of the defect related mechanism.