The effect of oxygen non-stoichiometry and doping with vanadium on the nature of magnetism in titanium dioxide with the anatase structure

The effect of oxygen non-stoichiometry and doping with vanadium on the electronic structure and magnetic properties of the titanium dioxide with the anatase structure have been studied by employing the tight-binding linear muffin-tin orbitals (TB-LMTO) method in the local spin-density approximation with the account of on-site Coulomb correlations (LSDA+U). It has been shown that the appearance of ferromagnetism in Ti1−xVxO2−y, Ti1−2xV2xO2−y compounds with 0≤x≤1/16, 0≤y≤1/16 is favored by the oxygen non-stoichiometry and location of the exchange-coupled vanadium atoms in the ac and bc planes of the crystal structure. At the vanadium concentration of 0.125 the super-exchange mechanism of the ferromagnetism is essential, with the Curie temperature (340 K) being in good relation to experimental data. The calculations demonstrate that the probability of formation of magnetic polarons is high at the vanadium concentration of 0.0625, but low at the concentration of 0.125. The reduction of magnetic moment with the rise of vanadium concentration corresponds to the general trend revealed for dilute magnetic semiconductors. It was established that the mechanisms of the high-temperature ferromagnetism in Ti1−xVxO2−y, Ti1−2xV2xO2−y compounds are different and depend on oxygen non-stoichiometry and vanadium concentrations.