Defect-Bound Carrier Mediated Room-Temperature Ferromagnetism in Co-Doped ZnO Powders

We prepare pure single-phase Co:ZnO powders introducing controllable
interstitial Zn_i by Zn vapour annealing. The as-ground powder shows that no room-temperature ferromagnetism (RT-FM) exists, while the Zn vapour treated samples exhibit unambiguous RT-FM with a maximum magnetic moment of 0.2μ_B/Co. The FM of Co:ZnO strongly depends on the Zn diffusion process, suggesting that not only carriers but also Zn_i defects play an important role in mediating FM in diluted magnetic semiconductors. A new core-shell model is proposed to interpret the mixture behaviour of FM and paramagnetism observed in the Zn vapour annealed Co:ZnO powders.