AlTiOsMn quaternary Heusler alloy: A half-metallic ferromagnet with promising spin-caloritronic properties

The equiatomic quaternary Heusler alloy AlTiOsMn exhibits a pronounced correlation-induced transition from a metallic ferromagnet to a half-metallic state, accompanied by thermally stable spin-selective transport. The ferromagnetic Type 3 configuration is the lowest-energy arrangement, with a lattice parameter of 6.06 Å and an energy above the convex hull of 0.037 eV/atom. Phonon calculations and ab-initio molecular dynamics support dynamical and thermal stability, while the lattice thermal conductivity decreases from 16.75 W/mK at 300 K to 5.39 W/mK at 900 K. Most importantly, the self-consistent Hubbard correction transforms the GGA metallic state into a half-metallic ferromagnet with a 0.19 eV half-metallic gap, 100% spin polarization, and a total magnetic moment of 4 μB. This electronic reconstruction is accompanied by a distinct spin-dependent thermoelectric response, with S_sp reaching about 78 μV/K and ZT_sp attaining 0.27 at 900 K in GGA and 0.23 in GGA + U. The results establish a direct link between correlation-driven half-metallicity and spin-selective thermoelectric transport, highlighting AlTiOsMn as a promising candidate for spintronic and spin-caloritronic applications.