Electronic structures of Heusler alloy Co2FeAl1−xSix surface

We have calculated the electronic structures of Co2FeAl1−xSix(101) surface using first-principles method based on the density functional theory. Because of the surface effect, the minority spin band gap at the Fermi level disappears at the surface of bulk Co2FeAl1−xSix. However, beneath the surface, the minority spin gap opens at the Fermi level, which indicates that the electronic structures of Co2FeAl1−xSix(101) become close to that of bulk phase. Accordingly, the Co2FeAl1−xSix(101) surface is a composite tri-layer structure that corresponds to the weakening of half-metallic property in Co2FeAl1−xSix films. Even though, the spin polarization of Co2FeAl1−xSix(101) surface is still larger than that of Co2FeAl or Co2FeSi materials, making Co2FeAl1−xSix a promising spintronics material.