Effect of Ga-doping and oxygen vacancies on the ferromagnetism of TiO2 thin films

In this paper, we combine first principles calculations and experiments to investigate the influence of Gadoping and oxygen vacancies on the magnetic properties of rutile TiO2 films. Ga-doped TiO2 with few oxygen vacancies exhibits ferromagnetism at room temperature with a T-c near 350 K, which can be explained using a modified magnetic polaron model. The number of Ti3+ ions increases with increasing the oxygen vacancies concentration, which results in a larger magnetic moment along with a higher T-c in TiO2-delta film with the ferromagnetic and antiferromagnetic coupling. The saturation magnetic moment is enhanced in Ga-doped TiO2-delta due to the absence of antiferromagnetic coupling after Ga-doping. More electrons occupy nearby Ti sites giving rise to the Ti3+ moments. Our theoretical calculations suggest that the modified magnetic polaron model works well for the ferromagnetism of doped and undoped-TiO2-delta. Experimental results clearly show that the T-c is related to the oxygen vacancies concentration, which is a verification of the polaron percolation theory. (C) 2016 Elsevier B.V. All rights reserved.