Influence of defects on magnetism of Co-doped ZnO

Two kinds of Zn0.97Co0.03O powders were prepared by precursor thermal decomposition under different conditions. One grown at low temperature has a positive Curie–Weiss temperature Θ, while the other grown at high temperature has a negative Θ. Both of them contain oxygen vacancies. There are more shallow donors in the former than those in the latter. It is proposed that coexistence of oxygen vacancies and shallow donors is necessary to induce ferromagnetic coupling between Co ions.

▸ The increase of VO and decrease of shallow donors with rising preparation temperature for Zn0.97Co0.03O. ▸ Curie–Weiss temperature Θ changes sign. ▸ No hysteresis is observed. ▸ Positive Θ indicates the presence of ferromagnetic component. ▸ Coexistence of oxygen vacancies and shallow donors is necessary.