Investigations of the electronic and magnetic structures at Heusler alloy surface: Co2TiGe (0Â 0Â 1)

The structural, magnetic and half-metallic properties of the bulk and (0 0 1) surface of the Co2TiGe full-Heusler alloy are Investigated from the first-principles projector augmented wave potential within the generalized gradient approximation. For the bulk, our calculations indicate that the Co2TiGe full-Heusler alloy exhibits a half-metallic ferromagnet with a total magnetic moment of 2.00 μB per formula unit at the equilibrium lattice constant of 5.87 Å. As the Co2TiGe (0 0 1) surfaces are found to display corrugations because of the different relaxations of the surface atoms. From the analysis of the spin-polarized density of states, we found that the half-metallicity confirmed in bulk Co2TiGe compound is lost at the Co-Co termination due to the surface states located at the Fermi level, but still preserved at the Ti-Ti, Ge-Ge and Ti-Ge terminations (0 0 1) surfaces with the spin polarization 100%, with smaller band gap energy due to surface states located just below the Fermi level. Comparing the atomic magnetic moments at the Co2TiGe (0 0 1) surfaces and bulk values, we found large differences in values at the Co-Co terminated surface.