Surface Electronic Structures and Magnetism of a Full-Heusler Alloy Co2CrGa(001): A First-principles Study

Abstract

We have investigated the electronic structures and magnetism of a full Heusler alloy <TEX>$Co_2CrGa(001)$</TEX> surface by using the all-electron full-potential linearized augmented plane wave (FLAPW) method within the generalized gradient approximation (GGA). We considered two types of different terminations: the Co-terminated (Co-Term) and the CrGa-terminated (CrGa-Term) surfaces. From the calculated layer-projected density of states (LDOS), we found that the surface of the CrGa-Term shows nearly half-metallic character while that of the Co-Term is far from the half-metallic. For the Co-Term, the surface Co atom moves down to the bulk region by <TEX>$0.05{\AA}A$</TEX>, while the subsurface Cr and Ga atoms move up to the surface layer by 0.05 and <TEX>$0.01{\AA}$</TEX>, respectively. For the CrGa-Term, there is a large inward relaxation of the surface Ga atom <TEX>$(0.07{\AA})$</TEX>, but the relaxation of the surface Cr atom is very small <TEX>$(0.01{\AA})$</TEX>. The relaxations affect not much to the overall shapes of DOS for both terminations, but make the surface states of the surface Cr and Ga atoms for the CrGa-Term shift to higher energy that enhances the nearly half-metallic character of the CrGa-Term. The magnetic moments of the surface <TEX>$Cr(2.98{\mu}_B)$</TEX> in the CrGa-Term and the surface <TEX>$Co(1.17{\mu}_B)$</TEX> in the Co-Term were much increased compared to those of the inner-layers <TEX>$(1.79\;and\;0.77{\mu}_B)$</TEX>, respectively, while that of the subsurface Cr atom in the Co-Term was decreased to <TEX>$1.19{\mu}_B$</TEX>.