Effect of oxygen partial pressure on the local structure and magnetic properties of Co-doped ZnO films

Zn0.95Co0.05O films were prepared under different oxygen partial pressures (PO2) by inductively coupled plasma enhanced physical vapor deposition. The effect of PO2 on the local structure and magnetic properties was investigated. The x-ray absorption spectroscopy at the Co K-edge, Co L-edge, and O K-edge revealed that the main defects were oxygen vacancies when the films were deposited under very low PO2. The change from room-temperature ferromagnetism to paramagnetism was observed with increasing PO2. It was experimentally demonstrated that the oxygen vacancy defect is absolutely necessary to induce ferromagnetic couplings in Co-doped ZnO films.