Polycrystalline CrxZn1-xO films and powders were prepared by co-sputtering and sol-gel method, respectively. While room-temperature ferromagnetism was found in as-deposited films, the powders exhibited paramagnetism. Comparison of the structural and magnetic properties of the as-deposited, annealed, and powdered samples indicated that the interstitial Zn, together with Cr doping, played an important role in the ferromagnetic origin of Cr:ZnO. The ferromagnetism in films could be described by bound magnetic polaron models with respect to defect-bound carriers.

Role of Point Defects in Room-Temperature Ferromagnetism of Cr-Doped ZnO. Liu, H., Zhang, X., Li, L., Wang, Y.X., Gao, K.H., Li, Z.Q., Zheng, R.K., Ringer, S.P., Zhang, B., Zhang, X.X.: Applied Physics Letters, 2007, 91[7], 072511