Vacancy-induced room-temperature ferromagnetism in Ga–TiO2

Ga–TiO2 films were deposited by pulsed laser deposition. It is found that the as-deposited films demonstrate room-temperature ferromagnetism that depends on the doping concentration and oxygen partial pressure during the deposition processing. Analysis indicates that the ferromagnetism is not associated with the impurities, but with Ti vacancies, a finding that is verified by positron annihilation spectroscopy. In addition, the possible origins of the ferromagnetism appearing in TiO2 doped with other elements that possess various valence states, such as Na, Mg, Sn, Ta and W, is discussed.