Magnetic and optical properties of Al-doped anatase TiO2 (101) surface from density functional theory

The effects of Al-doping on the magnetic and optical properties of anatase TiO2 (101) surface have been investigated with LDA+U calculations. The incorporation of Al atom induces a total magnetic moment of 1.00 μB, which mainly originates from the hole in 2p orbital of the oxygen atom. The room-temperature ferromagnetism (RTFM) of doping on the surface is more stabilized than that of doping in bulk by the hole-mediated double exchange between the nearest neighbor O atoms. Besides, it is shown that the excess electron associated with the oxygen vacancy can be captured by the nearest Ti ion, which reduces the Ti4+-Ti3+ with a spin magnetic moment of 1.00 μB. The existence of oxygen vacancy changes the magnetic mechanism from hole-mediated to electron-mediated. Additionally, the impurity states introduced by Al doping are conducive to enhancing the visible light absorption.