Exchange mechanism of half-metallic ferromagnetism of TiO2 doped with double impurities: A first-principles ASW study

The electronic structure and ferromagnetic properties of rutile TiO2 doped with double-impurities Ti1−2xCrxMnxO2 has been investigated using first-principles calculations within the density-functional theory (DFT) and the local density approximation (LDA), functional for treating the effects of exchange and correlation. They were performed using the scalar-relativistic implementation of the augmented spherical wave (ASW). The advantages of doping TiO2 with double impurities instead of single impurities are the increase of the total moment of the system and the exhibition of the half-metallic ferromagnetic nature in Cr- and Mn-doped TiO2 rutile. These behaviors are due to the hybridization of Cr 3d states and nearest-neighboring O 2p states. The spin–spin interaction between magnetic impurities examined by the total energy between parallel and antiparallel aligned states indicated that the Cr and Mn impurities are energetically favorable to be parallel coupled, which mean that the ferromagnetic state is more stable than the ferrimagnetic one. We proposed a bond magnetic polarons (BMP) model, based on localized carriers, to explain the mechanism of ferromagnetism in these systems.