Ab initio study on magnetism at TiO2/SrTiO3 interface

• A model of heterointerface is built and studied by first-principle calculation.
• The n-type d0-ferromagnetism at the interface is proposed firstly.
• We find that the unexpected magnetism results from anion vacancy without doping.
• Our results provide a new explanation of d0-ferromagnetism in the experiments.

Using density functional theory calculations, we have studied the electronic structure and magnetic properties of the TiO2/SrTiO3 interface with oxygen vacancy. We find that the oxygen vacancy at the interface may be responsible for the unexpected ferromagnetism in pristine anatase TiO2 film grown on SrTiO3 substrate. Structural relaxation has a profound impact on the local magnetic moment. After relaxation, the system can transform from a low spin state into a high spin state with the increasing Ti–Ti bond length. Isolated oxygen vacancy produces a magnetic moment of 0.36 μB. The magnetic moment mainly comes from the d-orbitals of Ti atoms adjacent to the oxygen vacancy. We also find that the two oxygen vacancies at the interface are always coupled ferromagnetically.