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

The pure single phase of Zn_0.95Co_0.05O bulks is successfully prepared by solid-state reaction method. The effects of annealing atmosphere on room-temperature ferromagnetic behaviour for the Zn_0.95Co_0.05O 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/H₂ gas, indicating that the strong ferromagnetism is associated with high oxygen vacancies density. High saturation magnetization M_s=0.73μ_B/Co and coercivity H_c=233.8Oe are obtained for the Ar/H₂ 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).