Electronic structure and magneto-optic Kerr effect in ferromagnetic titanium oxyphosphates Li 0.50Co 0.25TiO(PO4): An ab-initio study

Abstract

The X-ray diffraction for Li 0.50Co 0.25TiO(PO 4), was used as a starting point to perform structural optimization by minimizing the forces acting on the atoms. We have performed a comprehensive theoretical study of electronic properties, including magneto-optic Kerr effect, of titanium oxyphosphates Li 0.50Co 0.25TiO(PO 4) in the ferromagnetic phase. The generalized gradient approximation (GGA) exchange-correlation potential was applied within the full potential linear augmented plane wave (FP-LAPW) method. The total energy of the ferromagnetic state is 0.72 eV less than that of the paramagnetic state. The total moment is found to be 2.99μ B with a major contribution of 2.47μ B coming from the Co atoms. In addition, we have calculated the total and partial densities of states. The electron charge densities and the bonding properties are analyzed and discussed. As a remarkable finding we note that the ferromagnetic Li 0.50Co 0.25TiO(PO 4), is semiconducting with energy gap of about 1.2 eV for the minority spin and as semi-metallic for the majority spin, in contrast to the paramagnetic Li 0.50Co 0.25TiO(PO 4) which shows metallic behavior. From the calculated results of band structure and density of states, the half-metallic character and stability of ferromagnetic state for Li 0.50Co 0.25TiO(PO 4) is determined. The bonding properties of the ferromagnatic Li 0.50Co 0.25TiO(PO 4) have been analyzed through the electronic spin charge density contours in the (1 0 0) and (1 1 0) planes. The Kerr rotation spectrum is controlled by σ2xy(ω) at low energies (1.5-3.0 eV) because σ1xx(ω) is almost constant. The value of the Kerr rotation is close to 0.1 degree at low energies.