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 (Po-2) by inductively coupled plasma enhanced physical vapor deposition. The effect of Po-2 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 Po-2. The change from room-temperature ferromagnetism to paramagnetism was observed with increasing Po-2. It was experimentally demonstrated that the oxygen vacancy defect is absolutely necessary to induce ferromagnetic couplings in Co-doped ZnO films.