Ferromagnetism of Cu-doped anatase TiO2: the first-principles calculation study

The electronic structures and magnetic properties of Cu-doped anatase TiO2 have been investigated by first-principles calculations based on the density functional theory (DFT). Calculation results indicated that one Cu-substituted Ti (Cu@Ti) defect can introduce a total magnetic moment of 1 μB, which mainly distributed on the doped Cu atom and six neighboring oxygen atoms. In accordance with the group theory, the fivefold Cu-3d energy level splits into one threefold t2g orbital and one twofold eg orbital under the octahedral crystal field formed by the six neighboring oxygen atoms. The asymmetric electron occupation of the eg orbital generates a magnetic moment. The magnetic coupling between such two Cu@Ti defects is ferromagnetic, and the ferromagnetic energy advantage is 149 meV compared with the antiferromagnetic one. The larger energy difference means that the ferromagnetic coupling between the Cu@Ti defects is stable even at room temperature. The origin of ferromagnetism can be explained using the double-exchange model.