Ferromagnetic fluctuations in thermoelectric Heusler alloy Fe₂VAl: A weak-coupling approach

To study the enhanced thermopower by ferromagnetic fluctuations in Heusler compound Fe₂VAl, its low-energy effective model is numerically investigated by a weak-coupling theory. Recently, it is experimentally observed in doped Fe₂VAl that the thermoelectric properties such as the Seebeck coefficient and power factor are enhanced around the Curie temperature. In this study, first-principles calculations based on the density functional theory (DFT) are performed and then a 19-orbital model of Fe₂VAl is constructed by the maximally localized Wannier functions. The obtained tight-binding model includes the Fe-3d, V-3d, and Al-3sp3 orbitals and the energy band structure reproduces the original DFT band structure around the Fermi level. Furthermore, the 19-orbital Hubbard model is considered by adding interaction terms to the tight-binding model and investigated by the random phase approximation. The spin susceptibility shows the ferromagnetic instability at the low temperatures around the original band filling. In our presentation on the day, we also plan to report on the numerical evaluation of the thermoelectric performance.