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. Zhan, P., Wang, W., Liu, C., Hu, Y., Li, Z., Zhang, Z., Zhang, P., Wang, B., Cao, X.: Journal of Applied Physics, 2012, 111[3], 033501