The influence of hydrogen annealing on magnetism of Co-doped TiO2 films prepared by sol–gel method

Abstract Co-doped TiO 2 (Co x Ti 1− x O 2 , 0.05⩽ x ⩽0.2) films have been prepared on Si (0 0 1) substrates by sol–gel method. When heat treated in air, Co x Ti 1− x O 2 films are non-ferromagnetic at room temperature. However, after further annealed in a flowing hydrogen atmosphere, Co x Ti 1− x O 2 films show room-temperature ferromagnetism (RTFM). Measurements of magnetization ( M ) vs. temperature ( T ), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) fail to detect Co clusters in the hydrogenated Co 0.1 Ti 0.9 O 2 films, suggesting that RTFM in the hydrogenated Co 0.1 Ti 0.9 O 2 films may be intrinsic. But, metal Co appears in the hydrogenated Co 0.2 Ti 0.8 O 2 films, showing that RTFM in the hydrogenated Co 0.2 Ti 0.8 O 2 films is as least partly due to metal Co. These results indicate that hydrogen annealing can produce room-temperature ferromagnetism in Co x Ti 1− x O 2 films, but it should be carefully designed to avoid the formation of metal Co in the hydrogenated Co x Ti 1− x O 2 films.