The effects of oxygen vacancies upon the magnetic properties of anatase Fe-doped TiO2 compound were investigated. The air-annealed sample exhibited a small magnetic moment at room temperature, whereas the magnetic moment at same temperature was strongly enhanced for the sample post-annealed in vacuum ambience. Mössbauer spectra of air-annealed sample showed that the magnetically ordered sextet and paramagnetic doublet co-existed in all temperature ranges (4.2-295K), where all Fe ions were not metallic but in the +3 state substituting for Ti. After vacuum annealing, an additional doublet appeared with large quadrupole splitting, which was consistent with Fe2+ state. This result suggests that the enhancement of magnetic moment after vacuum annealing was attributable to the moment by the spin-orbit coupling of Fe2+ ions.

Effects of Oxygen Vacancies on the Ferromagnetism in Fe-Doped Anatase TiO2. Lee, H.M., Kim, C.S.: Journal of Magnetism and Magnetic Materials, 2007, 310[2], 2099-101