Using the full-potential linearized augmented plane wave method, an investigation was made of the oxygen vacancy defect-induced ferromagnetism in both rutile and anatase. It was found that the oxygen vacancy introduced a lattice distortion into rutile, whereas there was no such significant change in the anatase structure. The lattice-distorted rutile exhibited an oxygen vacancy-induced ferromagnetic state with a magnetic moment of 0.22µB in the Ti atom neighbouring the vacancy site, while only 0.06µB was observed for the Ti atom in anatase. The sizable magnetic moment due to the oxygen vacancy in rutile was attributed to the charge redistribution due to lattice distortion. Experimentally measured magnetic hysteresis curves for undoped rutile and anatase films clearly revealed a ferromagnetic behaviour at room temperature. The observed magnetic strength of the rutile samples was found to be larger than that of the anatase samples; in accord with the theoretical calculations.

The Origin of Oxygen Vacancy Induced Ferromagnetism in Undoped TiO2. Kim, D., Hong, J., Park, Y.R., Kim, K.J.: Journal of Physics - Condensed Matter, 2009, 21[19], 195405