Structure and composition of secondary phase particles in cobalt-doped TiO ₂ films

The microstructural properties of secondary phase particles formed in epitaxial Co _xTi _1-xO ₂ anatase thin films grown on (0 0 1)LaAlO ₃ by a reactive RF magnetron co-sputter deposition are examined. These films exhibit ferromagnetic behavior in magnetization measurements, showing a M-H loop at room temperature with a saturation magnetization on the order of 0.7 μ _B /Co. X-ray photoemission spectrometry indicates that the Co cations are in the Co ²⁺ valence state. Cross-section electron microscopy reveals that a significant fraction of the cobalt segregates into Co-Ti-O secondary phase particles. Selected area electron diffraction shows that the secondary phase particles are cobalt-rich anatase. While the cobalt is concentrated in the segregated particles, local energy dispersive spectrometry indicates some Co throughout the film.