Properties of anatase CoxTi1−xO2 thin films epitaxially grown by reactive sputtering

Epitaxial CoxTi1−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 CoxTi1−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 CoxTi1−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.