Effects of oxygen vacancies on the ferromagnetism in Fe-doped anatase TiO2

Abstract Effects of oxygen vacancies on the magnetic properties of anatase Fe-doped TiO2 compound have been investigated. The air-annealed sample shows a small magnetic moment at room temperature, whereas the magnetic moment at same temperature is strongly enhanced for the sample post-annealed in vacuum ambience. Mossbauer spectra of air-annealed sample show that the magnetically ordered sextet and paramagnetic doublet coexist in all temperature ranges (4.2–295 K), where all Fe ions are not metallic but in the +3 state substituting for Ti. After vacuum annealing, an additional doublet appeared with large quadrupole splitting, which is consistent with Fe2+ state. This result suggests that the enhancement of magnetic moment after vacuum annealing is attributable to the moment by the spin–orbit coupling of Fe2+ ions.