Origin of Room-Temperature Ferromagnetism for Cobalt-Doped ZnO Diluted Magnetic Semiconductor

The pure single phase of Zn 0.95 Co 0.050 bulks is successfully prepared by solid-state reaction method. The effects of annealing atmosphere on room-temperature ferromagnetic behaviour for the Zn 0.95 Co 0.05 O bulks are investigated. The results show that the air-annealed samples has similar weak ferromagnetic behaviour with the as-sintered samples, but the obvious ferromagnetic behaviour is observed for the samples annealed in vacuum or Ar/H 2 gas, indicating that the strong ferromagnetism is associated with high oxygen vacancies density. High saturation magnetization M s = 0.73 μ B /Co and coercivity H c = 233.8 Oe are obtained for the Ar/H 2 annealed samples with pure single phase structure. The enhanced room-temperature ferromagnetic behaviour is also found in the samples with high carrier concentration controlled by doping interstitials Zn (Zn i ).