Properties of anatase Co_xTi_1-xO₂ thin films epitaxially grown by reactive sputtering

Epitaxial Co_xTi_1-xO₂ anatase thin films were grown on (001)LaAlO₃ by a reactive RF magnetron co-sputter deposition with water vapor serving as the oxidant. The use of water as the oxygen source proves useful in growing oxygen-deficient, semiconducting Co _xTi_1-xO₂ by reactive sputter deposition, with undoped and Co-doped TiO₂ thin films showing n-type semiconductor behavior, with carrier concentrations of 10¹⁷-10¹⁸ cm ^-3. Magnetization measurements of Co_xTi _1-xO₂ (x = 0.07) thin films reveal ferromagnetic behavior in M-H loop at room temperature with a saturation magnetization on the order of 0.7 Bohr magnetons/Co. X-ray photoemission spectrometry indicates that the Co cations are in the Co²⁺ valence state. However, chemical analysis of surface structure indicates that a significant fraction of the cobalt segregates into a Co-Ti-O phase. This suggests that the ferromagnetic moments may reside in oxygen-bound Co that is segregated from the majority anatase phase.