Structural defects-mediated room-temperature ferromagnetism in Co-doped SnO2 insulating films

Co-doped SnO2 insulating films with different crystal quality were fabricated using magnetron sputtering. X-ray photoelectron spectroscopy and X-ray absorption near-edge structure spectrum reveal a solid solution of Co dopants in SnO2 lattice, where Co is in 2+ oxidation state and substitutes for Sn4+. The as-grown films with different crystallinity exhibit clearly room-temperature ferromagnetism, and the films with more structural defects show higher saturated magnetic moment. With the increase of annealing time, the crystallinity of the films is improved and the defects decrease, leading to the decrease or disappearance of ferromagnetism in the films. The results show that the ferromagnetism in Co-doped SnO2 films is intrinsic and can be considerably influenced by the concentration of structural defects.