The Electronic Structures, Magnetism And Half-Metallicity Of Heusler Alloy Co₂FeSi Surface: First-Principles Study

Spintronics is a new interactive-type subject in recent years; it mainly explores the transport and storage of information by electron spin. In spintronics, the Half-metallic alloy attracts great attentions, because it could improve electron spin polarization when the alloy injects into the semiconductor. In present, the Full-Heusler alloy Co2FeSi has the highest magnetic moment and Curie temperature in the reported many ferromagnet materials. It is considered an ideal source of spin injection.In this paper, by the full-potential linearized augmented plane wave (FLAPW) method within the generalized gradient approximation (GGA) and plus on-site coulo-mb exchange interaction U, we have investigated the electronic structures, magnetism and half-metallicity of the Full-Heusler alloy Co2FeSi (001) surface. For [001] directi-on, we have considered two types of surfaces:the Co atoms terminated and the Fe and Si atoms terminated surfaces. The results are followings:(1) Co atoms terminate surface will loss the half-metallicity. It was found that the minority-spin states of Co (surface) atoms were localized and moved to higher energy from lower energy, which destroys the minority spin band gap due to the reduced coordination number of Co (surface) atoms. The calculated spin polarizations of the surface layer are negative with values of-48.3%(U75) and-43.2%(U10). The magnetic moment (～1.75μB) of the surface Co atom is larger than that (～1.51μB) of the inner layer because of the reduced coordination number of Co (surface) atom, which increases the exchange splitting at the surface. The magnetic moment (～3μB) of the subsurface Fe atom decreased slightly than that (～3.15μB) of the center layer due to increased covalent hybridization between the Fe (subsurface) and the Co (surface) atoms.(2) Fe and Si atoms terminated surface also loss the half-metallicity. At the surface the coordination number of Fe (surface) atoms was reduced from 8 to 4 Co atoms. It was found that the unoccupied minority-spin states of surface Fe atoms shifted from higher energy to lower energy, and the surface states appear in the band gap. The calculated spin polarizations for the surface layers are negative with values of-87.3%(U7.5) and-43.2%(U10). The magnetic moment (～3.28μB) of surface Fe is slightly larger than the value (～3.14μB) of the inner layer due to the increase of the exchange splitting at the surface. On the other hand, the magnetic moment of subsurface Co atom is similar to that of the inner layer Co atom.