Origin of magnetic moments in defective TiO2 single crystals

In this Brief Report we show that ferromagnetism can be induced in pure TiO2 single crystals by oxygen ion irradiation. By combining x-ray diffraction, Raman scattering, and electron-spin resonance spectroscopy, a defect complex, i.e., Ti3+ ions on the substitutional sites accompanied by oxygen vacancies, has been identified in irradiated TiO2. This kind of defect complex results in a local (TiO6-x) stretching Raman mode. We elucidate that Ti3+ ions with one unpaired 3d electron provide the local magnetic moments.