Room-temperature ferromagnetism observed in undoped semiconducting and insulating oxide thin films

Remarkable room-temperature ferromagnetism was observed in undoped TiO_2, HfO_2, and In_2O_3 thin films. The magnetic moment is rather modest in the case of In_2O_3 films on MgO substrates (while on Al_2O_3 substrates, it is negative showing diamagnetism) when the magnetic field was applied parallel to the film plane. In contrast, it is very large in the other two cases (about 20 and 30 emu/cm^3 for 200-nm-thick TiO_2 and HfO_2 films, respectively). Since bulk TiO_2, HfO_2, and In_2O_3 are clearly diamagnetic, and moreover, there are no contaminations in any substrate, we must assume that the thin film form, which might create necessary defects or oxygen vacancies, would be the reason for undoped semiconducting or insulating oxides to become ferromagnetic at room temperature