The role of oxygen vacancies in magnetism of CoxTi1−xO2−δ films on Si(001) prepared by sol-gel method

CoxTi1−xO2−δ films have been prepared on Si(001) substrates by sol-gel method. When heat treated in air, CoxTi1−xO2−δ films are non-ferromagnetic at room temperature. However, after further vacuum annealing or hydrogenation, CoxTi1−xO2−δ films show room-temperature ferromagnetism (RTFM). When the vacuum annealed CoxTi1−xO2−δ films are reheated in air, the magnetic moments of the films strongly reduce. After these films are vacuum annealed once again, the magnetic moments are greatly enhanced, confirming the role of vacuum annealing in ferromagnetism of CoxTi1−xO2−δ films. The x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS) and measurements of magnetization (M) vs temperature (T) fail to detect Co clusters in the vacuum annealed and the hydrogenated CoxTi1−xO2−δ films. Oxygen vacancies are formed in CoxTi1−xO2−δ films after vacuum annealing and hydrogenation, determined by XRD and XPS measurements. These results indicate that oxygen vacancies created by vacuum annealing and hydrogenation play an important role in the generation of RTFM in CoxTi1−xO2−δ films.