Co-doped TiO₂ epitaxial thin films grown by sputtering

Co-doped TiO₂ anatase thin films were epitaxially grown by sputtering. It is found that the films have good epitaxial structure and contain single anatase phase. Co in the films is in + 2 oxidation state. However, there are also pure metal Co clusters on the film surface. Saturation moments (m _s) of films are found to be independent of carrier density, which implies that the carriers are unimportant for the ferromagnetism in these Co-doped TiO₂ anatase films. Neither an anomalous Hall effect nor a characteristic magnetoresistance are observed even at a temperature down to 2.2 K, which indicates that Co-doped anatase films may not be an intrinsic magnetic semiconductor.