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 (ms) 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.