Spin-polarized linear dispersions, lattice dynamics and transport properties of quaternary Heusler alloys (LiMgXSb)

In this study, we are predicting a new class of materials obtained by substituting a magnetic transition metal ion in quaternary Heusler alloys with the formula LiMgXSb (X = Co, Cr, Fe, Mn). We found that all the studied alloys exhibit a ferromagnetic ground state except LiMgCoSb. The phonon dispersions of the studied alloys computed within spin-polarized density functional perturbation theory (DFPT) do not exhibit any imaginary frequencies indicating that the proposed alloys are dynamically stable. The band structure calculations show that the studied alloys are metallic and exhibit the states near Fermi level for both spins. The fixed spin moment (FSM) calculations have been employed to exclude the possibility of other ferromagnetic ground states. One of the most interesting aspects of the band structure of these compounds is the existence of multiple band crossings leading to multiple Weyl points in the Brillouin zone. We have also computed the spin-polarized transport properties of these alloys. Our results find that doping charge carriers in the unit cell can significantly enhance the power factor and ZT. Electron doping is more effective for improving the power factor. Our findings show that among all the alloys LiMgFeSb has the highest ZT value with electron doping. Our studied materials constitute a new family of three-dimensional materials exhibiting band degeneracies that lead to Weyl points.