The role of oxygen vacancies in magnetism of Co xTi 1− xO 2−δ films on Si(001) prepared by sol–gel method

Abstract

Co x Ti 1− x O 2−δ films have been prepared on Si(001) substrates by sol–gel method. When heat treated in air, Co x Ti 1− x O 2−δ films are non-ferromagnetic at room temperature. However, after further vacuum annealing or hydrogenation, Co x Ti 1− x O 2−δ films show room-temperature ferromagnetism (RTFM). When the vacuum annealed Co x Ti 1− x O 2−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 Co x Ti 1− x O 2−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 Co x Ti 1− x O 2−δ films. Oxygen vacancies are formed in Co x Ti 1− x O 2−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 Co x Ti 1− x O 2−δ films.