Films became ferromagnetic when defects were introduced by thermal-annealing in flowing argon. This ferromagnetism, as shown by the photoluminescence measurement and positron annihilation analysis, was induced by the singly occupied oxygen vacancy with a saturated magnetization dependent positively on the amount of this vacancy. This study clarified the origin of the ferromagnetism of un-doped ZnO thin films and provides possibly an alternative way to prepare ferromagnetic ZnO films.

Oxygen Vacancy–Induced Ferromagnetism in Un-Doped ZnO Thin Films. P.Zhan, W.Wang, C.Liu, Y.Hu, Z.Li, Z.Zhang, P.Zhang, B.Wang, X.Cao: Journal of Applied Physics, 2012, 111[3], 033501