Abstract
Using the full-potential linearized augmented plane wave method, we have investigatedthe oxygen vacancy defect induced ferromagnetism in both rutile and anataseTiO2. It has been found that the oxygen vacancy induces lattice distortion in rutileTiO2,whereas there is no such meaningful change in the anatase structure. Interestingly, the lattice distortedrutile TiO2 shows an oxygen vacancy induced ferromagnetic state with a magnetic moment of0.22 µB in the Ti atom neighboring the vacancy site, while only0.06 µB is observed in theTi atom in anatase TiO2. We attribute the sizable magnetic moment due to the oxygen vacancy in rutileTiO2 to the charge redistribution owing to lattice distortion. Experimentallymeasured magnetic hysteresis curves for undoped rutile and anataseTiO2 films clearly display ferromagnetic behavior at room temperature. The observed magneticstrength of the rutile sample turns out to be larger than that of the anatase sample, inaccordance with the theoretical calculations.
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