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

We prepare pure single-phase Co：ZnO powders introducing controllable interstitial Zni 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 0.2μB/Co. The FM of Co：ZnO strongly depends on the Zn diffusion process, suggesting that not only carriers but also Zni 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.