First-principles study of the electronic and magnetic properties of oxygen-deficient rutile TiO2(1 1 0) surface

Based on first-principles electronic structure calculations we find that the bridging oxygen vacancies on the (1 1 0) surface is more favorable and may be responsible for the unexpected ferromagnetism in undoped rutile TiO₂. Our results show that the ferromagnetism largely originates from the d orbitals of low-charge-state Ti ions converted from Ti⁴⁺ ions induced by the surface oxygen vacancies. The second-nearest neighbors of these ions (fivefold coordinated Ti) also contribute to the total magnetic moments. The spins induced by the local oxygen vacancies form a ferromagnetic arrangement.