Ferromagnetism enhancement by increasing oxygen vacancies in Co-doped ZnO thin films

In the reported study, thin films of ZnO doped with 10 wt. % Co were fabricated by pulsed laser deposition under different oxygen partial pressures. The results of x-ray photoelectron spectroscopy show that the valence state of the Co ions is 2+ and that the number of oxygen vacancies is increased by lowering the oxygen partial pressure during deposition. The results of UV–visible absorption spectroscopy show that the Co2+ ions substitute for the Zn sites in the ZnO lattice. Ferromagnetism in the Co-doped ZnO thin films is observed up to 300 K. Furthermore, the saturation magnetization increases as the oxygen partial pressure decreases, indicating a strong correlation between the number of oxygen vacancies and the saturation magnetization. This suggests that ferromagnetism in Co-doped ZnO can be enhanced by simply controlling the oxygen partial pressure that causes oxygen vacancies. Furthermore, how the mechanism for the expression of ferromagnetism can be explained by the bound magnetic polaron model is discussed.