Oxygen vacancy induced ferromagnetism in un-doped ZnO thin films

ZnO 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.