Surface and correlation effect on the half-metallicity of the Co2FeSi Heusler alloy

We report the ab-initio calculational results for the half-metallicity of the Co2FeSi full Heusler alloy in (001) surfaces. Employing the +U corrections, in addition to the local density approximation (LDA) and generalized gradient approximation (GGA), we investigate the effects of surface and correlation interactions on the half-metallicity and the magnetic properties. The (001) surfaces are calculated to be metallic by both the LDA and the GGA due to the surface states the develop at the Fermi energy (EF). Upon +U correction, the surface states are pushed down below EF for the Co-terminated surface, which recovers the half-metallicity with a reduced band gap of 0.40 eV. In contrast, the FeSi-terminated surface is predicted to be metallic because the surface states remain at the Fermi level in spite of an enhanced t2g−eg band splitting caused by the correlation effect.