Reversible ferromagnetism study in un-doped ZnO thin film

Room temperature ferromagnetism in pure ZnO thin film prepared by sol-gel spin-coating method was observed, together with the obvious anisotropic property. In order to study the origin of ferromagnetism, ZnO thin films were rapidly annealed in N₂ and O₂ ambient in a repetitive way. Electrical and magnetic performance after each annealing was measured. It was found that ferromagnetism was quenched and re-appeared, in accordance with the decrease and increase of conductivity. These results provide further evidence that oxygen vacancies play a significant role in inducing ferromagnetism in ZnO thin films.