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

Abstract

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 μV 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 Γ 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.