Ferromagnetism in laser deposited anatase Ti_1-xCo_xO_2-δ films

Abstract

Pulsed laser deposited films of Co-doped anatase TiO₂ 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_0.93Co_0.07O_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_0.99Co_0.01O_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-xCo_xO_2-δdiluted magnetic semiconductor with T_C of about 650-700 K.