Insight into half-metallicity, electronic structure, and thermal transport properties of FeRhGa1−xAsx Heusler alloys

In this work, we study electronic structure, magnetic, and transport properties of FeRhGa${}_{1-x}$As${}_x$ half-Heusler alloys ($0\le x\le 1$) using the extensive density functional calculations. We find that the ground state of compounds with $0\le x\le 0.75$ is the cubic $\gamma$ phase, while FeRhAs possesses the cubic $\beta$ phase. The main difference between the two structures is an occupation of four by 8 tetrahedral sites by Ga and Rh, respectively. The mechanical and thermodynamic stability of the ground state structures is confirmed using the predicted elastic constants and phonon spectra. The parent FeRhGa and FeRhAs alloys demonstrate 66 and 74 % spin polarization, respectively, while FeRhGa_0.5As_0.5 reveals the robust half-metallic behavior. In this case, the 100 % spin polarization is retained under compressive pressure up to 5 GPa. The FeRhGa_0.5As_0.5 alloy possesses the thermal conductivity (${\kappa }_{lat}\approx 11$ W/(m$\times$K)), whereas the parent compounds FeRhGa and FeRhAs are characterized by ${\kappa }_{lat}$ of 12.7 and 7.45 W/(m$\times$K) at 300 K, correspondingly. To explore the possible thermoelectric properties achievable in half-metallic FeRhGa_0.5As_0.5, we investigate the relationship between the optimal carrier concentration, power factor, and figure of merit $ZT$. It is shown that for $n$-type doping about 10²² cm⁻³, FeRhGa_0.5As_0.5 demonstrates several times higher thermoelectric properties than those of $p$-type doping especially in a case of the temperature dependent relaxation time approach. Our results pave the way for further research into FeRhGa${}_{1-x}$As${}_x$ alloys in the search for improved spintronic and thermoelectric materials for use in applications where high spintronic and thermoelectric performance is required.