Impurity concentration study on ferromagnetism in Cu-doped TiO2 thin films

We report here the observation of significant room-temperature ferromagnetism in a semiconductor doped with nonmagnetic impurities, Cu-doped rutile TiO2 thin films grown by reactive magnetron sputtering. Films annealed in air were nonmagnetic while those annealed in vacuum were ferromagnetic with a Curie temperature about 350 K. The magnetic moment per copper atom decreased as the copper concentration increased. These results show that both the oxygen vacancies and the distance between nearest-neighbor copper atoms play a crucial role for the appearance of magnetism.