Defect types and room-temperature ferromagnetism in undoped rutile TiO2 single crystals

Room-temperature ferromagnetism has been experimentally observed in annealed rutile TiO2 single crystals when a magnetic field is applied parallel to the sample plane.By combining X-ray absorption near the edge structure spectrum and positron annihilation lifetime spectroscopy,Ti^3＋-V O defect complexes（or clusters） have been identified in annealed crystals at a high vacuum.We elucidate that the unpaired 3d electrons in Ti^3＋ ions provide the observed room-temperature ferromagnetism.In addition,excess oxygen ions in the TiO2 lattice could induce a number of Ti vacancies which obviously increase magnetic moments.