X-ray absorption near-edge structure spectroscopy and first-principles calculations were combined in order to study the local and electronic structures of rutile Co:TiO2 thin films exhibiting room-temperature ferromagnetism. It was revealed that CoTi2+, substituted at Ti sites, formed a CoTi2+-VO complex, with the O vacancy being generated in the annealing process. The O vacancy introduced a spin-split donor impurity band with a t2g character within the gap region. It was proposed that the strong exchange interaction between the localized carriers captured by the O vacancy and the substitutional Co ions led to the ferromagnetism of the Co:TiO2 thin films.

Oxygen Vacancy Effect on Room-Temperature Ferromagnetism of Rutile Co:TiO2 Thin Films. Yan, W., Sun, Z., Pan, Z., Liu, Q., Yao, T., Wu, Z., Song, C., Zeng, F., Xie, Y., Hu, T., Wei, S.: Applied Physics Letters, 2009, 94[4], 042508