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

Co-doped TiO2 (CoxTi1−xO2, 0.05⩽x⩽0.2) films have been prepared on Si (0 0 1) substrates by sol–gel method. When heat treated in air, CoxTi1−xO2 films are non-ferromagnetic at room temperature. However, after further annealed in a flowing hydrogen atmosphere, CoxTi1−xO2 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 Co0.1Ti0.9O2 films, suggesting that RTFM in the hydrogenated Co0.1Ti0.9O2 films may be intrinsic. But, metal Co appears in the hydrogenated Co0.2Ti0.8O2 films, showing that RTFM in the hydrogenated Co0.2Ti0.8O2 films is as least partly due to metal Co. These results indicate that hydrogen annealing can produce room-temperature ferromagnetism in CoxTi1−xO2 films, but it should be carefully designed to avoid the formation of metal Co in the hydrogenated CoxTi1−xO2 films.