Diluted ferromagnetic properties in Fe- and Co-doped TiO2-δ thin films

Magnetic and electronic properties of Fe- and Co-doped TiO_2-δ thin films are investigated by vibrating sample magnetometer (VSM), Mossbauer spectroscopy, and X-ray photoelectron spectroscopy (XPS). When the precursor films are annealed in vacuum, the resulting oxygen-deficient TiO_2-δ:Fe and TiO_2-δ:Co films are found to become semiconducting with p-type carriers in the 10¹⁸ cm^-3 range. The oxygen-deficient films go through conductivity transitions from n-type to p-type by Fe and Co doping. Results of VSM measurements show that ferromagnetism is exhibited at room temperature. XPS measurements on the thin films reveal that Fe ions have both Fe²⁺ and Fe³⁺ ionic valences while Co ions have Co²⁺ mostly. Also, the density of Fe²⁺ ions is found to decrease after annealing.