Electronic structure and magnetic properties of two-dimensional nonstoichiometric rutile

The coherent potential approximation is applied to study the influence of vacancies in the oxygen lattice on the electronic structure and magnetic properties of the TiO1.99 rutile (110) surface. Stoichiometric two-dimensional rutile is found to be a nonmagnetic semiconductor. Vacancies in the oxygen positions on the surface lead to the metallic type of the electronic spectrum. Additionally, they result in the appearance of spin magnetic moments on titanium atoms surrounded by only five oxygen atoms due to the surface formation. The vacancies in all the other oxygen positions except of the surface cause a nonmagnetic semiconducting character of the energy spectrum of two-dimensional TiO1.99. A mechanism that underlies the formation of spin magnetic moments of the titanium atoms, namely Stoner ferromagnetism of a defect related impurity band, is discussed.