First-principles Study On Magnetic And Optical Properties Of Rutile TiO₂

The magnetic and optical properties of N- and Co- doped rutile TiO₂, together with (N, Co) co-doped rutile TiO₂ have been investigated by first-principle, which were based on the full potential linearized augmented plane wave (FPLP) method within the density functional theory (DFT).The results are analyzed and discussed profoundly:(1) For the non-magnetic element N doped in TiO₂, the 2×1×1 supercell containing 12 atoms is established, in which the doping concentration is 12.5%. The total magnetic moment of the material is 0.960μ_B, which mainly originates from impurity atom N, since on the one hand, the electron which resides in p orbital yields an impuritical level in forbidden band, on the other hand, the electron which resides in s orbital brings into a deep impuritical level in valence band. In addition, the ability of optical absorption of TiO₂ with doping N atom in the range of visible light is enhanced.(2) For the magnetic element Co doped in TiO₂, we establish a 2×2×1 supercell containing 24 atoms, wherein the doping concentration is also 12.5%. The total magnetic moment is 1.03μ_B,which is mainly attributed to the impuritical atom Co. It shows that the electron localized in d orbital of Co atom is responsible for the total density of states in the fermi surface. Besides, the ability of optical absorption of TiO₂ with doping Co atom in the range of visible light is also enhanced. Furthermore, the absorped wavelength becomes longer because of the emergence of the impuritical energy band, resulting in the reduce of the energy gap.(3) For the (Co, N) co-doped in TiO₂, the 2×2×1 supercell containing 24 atoms is established, where the doping concentrations of N and Co are 6.25% and12.5%, respectively. Herein, we obtain the total magnetic moment with its value 0.916μ_B.It presents half-metal-like property because of the existence of p-d orbitals hybridization between N and Co atoms, giving rise to the splitting of the energy bands near the Fermi level. Although the energy gap is reduced due to the appearance of the impuritical level, the ability of optical absorption in the region of visible light is weaker than Co doped in TiO₂ purely because of the complex mutual interactions between the impuritical atoms.