The effect of donor localization on the magnetic properties of Zn–Co–O system was investigated by resonant inelastic x-ray scattering and first principle calculations. It was found that the ferromagnetic coupling was induced through charge transfer between Co 3d and donor defect. The charge transfer was dependent on the electron localization of donor defect. The electron localization of oxygen vacancy defect was much stronger than that of donor defect formed by the substitution of Al3+ for Zn2+. In order to elucidate the magnetic mechanism, a series of Zn0.95Co0.05O and Zn0.94Co0.05Al0.01O films were prepared under different oxygen partial pressure (PO2). The magnetic properties of Zn0.95Co0.05O films were dependent on PO2, while Zn0.94Co0.05Al0.01O films showed stable ferromagnetism.

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