Ferromagnetism in laser deposited anatase Ti 1-x Co x O 2-δ films

Pulsed laser deposited films of Co-doped anatase TiO 2 are examined for Co substitutionality, ferromagnetism, transport, magnetotransport, and optical properties. Our results show limited solubility (up to ~2%) of Co in the as-grown films and formation of Co clusters thereafter. For the Ti 0.93 Co 0.07 O 2-δ sample, which exhibits a Curie temperature (T C ) over 1180 K, we find the presence of 20-50 nm Co clusters as well as a small concentration of Co incorporated into the remaining matrix. After being subjected to the high-temperature anneal during the first magnetization measurement, the very same sample shows a T C ~650K and almost full matrix incorporation of Co. This T C is close to that of as-grown Ti 0.99 Co 0.01 O 2-δ sample (~700 K). The transport, magnetotransport, and optical studies also reveal interesting effects of the matrix incorporation of Co. These results are indicative of an intrinsic Ti 1-x Co x O 2-δ diluted magnetic semiconductor with T C of about 650-700 K.