Transport properties of Co-based Heusler compounds Co2VAl and Co2VGa: spin-polarized DFT plus U

摘要

Transport properties of two Co-based Heusler compounds Co2VAl and Co2VGa were calculated. The calculated spin-polarized electronic band structures for majority and minority spin reveal that the minority spin exhibits an indirect band gap of about 0.3 eV for Co2VAl and 0.2 eV for Co2VGa. It is clear that the minority spin density of states at E-F, N(E-F) vanishes for Co2VAl and Co2VGa which leads to unusual transport properties because only the majority density contributes to the states at E-F. The calculated valence band's electronic charge density distribution reveals that there exists a strong covalent bond between the atoms which is more favorable for the transport of carriers than an ionic one. The transport properties were calculated as a function of temperature at a fixed chemical potential and as a function of chemical potential at three constant temperatures. In Co2VAl a large value (1100 mu V K-1) of Seebeck coefficient is obtained for spin-down electrons due to the existence of an almost flat conduction band along the L to Gamma direction. Calculations show that Co2VAl exhibits a higher Seebeck coefficient than that obtained from Co2VGa and the increase in the Seebeck coefficient also leads to a maximum in the power factor. This makes the Co2VAl and Co2VGa compounds attractive candidates for materials used in spin voltage generators.