Structure and composition of secondary phase particles in cobalt-doped TiO2 films

The microstructural properties of secondary phase particles formed in epitaxial Co_xTi_1−xO₂ anatase thin films grown on (0 0 1)LaAlO₃ 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 Co²⁺ 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.