Ferromagnetism in Cu-doped AlN films

AlN films doped with 3.2–8.2 at. % Cu were deposited by helicon magnetron sputtering. The films exhibited ferromagnetism with a Curie temperature above 360 K. The observed magnetic anisotropy and exclusion of ferromagnetic contamination indicated that the ferromagnetism was the intrinsic property of Cu-doped AlN films. Room-temperature (RT) saturation magnetization (Ms) tended to decrease with increasing Cu concentration and the maximum RT Ms obtained was about 8.5 emu/cm3 (0.6 μB/Cu). Vacuum annealing increased the RT Ms values and meanwhile reduced ratio of N/(Al+Cu), which suggested that Al interstitial and N vacancy might contribute to the observed ferromagnetic behavior.