Electronic transport properties and Microstructures of TiO2:Co magnetic semiconductors

TiO2:Co thin films of high Co concentration were investigated by the high resolution transmission electron microscopy, physical property measurement system and energy dispersive X-ray. The as-deposited films are amorphous magnetic semiconductors and we did not find any Co metal particles in them. The electronic transport process in the low-temperature range below 80K could be described by the spin-dependent variable-range-hopping process. However, after the samples were annealed at 300 deg C, large amounts of Co metal particles were observed to connect each other and the films show a metallic behavior. The origin of ferromagnetism of the thin films is also discussed.