First-principles study of structural, mechanical, electronic and magnetic properties of CoPtMnAl and FePtMnSi quaternary Heusler alloys for spintronic applications

Abstract This work presents a first-principles investigation of the structural, mechanical, electronic, magnetic, optical and thermoelectric properties of two quaternary Heusler alloys, CoPtMnAl and FePtMnSi. Analysis of the elastic constants confirms the mechanical stability of both alloys. Electronic-structure calculations predict robust half-metallic behaviour at the equilibrium lattice constants, characterised by 100% spin polarization at the Fermi level and an integer total magnetic moment of 5 μB per formula unit, in agreement with the Z—24 Slater–Pauling rule. The minority-spin band gaps are calculated to be 0.53 eV for CoPtMnAl and 0.52 eV for FePtMnSi. The calculated linear optical spectra indicate a metallic optical response, marked by strong low-energy screening and pronounced interband absorption in the IR and near-IR regions. FePtMnSi exhibits a more dissipative optical character, whereas CoPtMnAl is comparatively less lossy and shows slightly higher reflectivity in parts of the visible spectrum. Boltzmann transport calculations predict metallic, n-type transport for both alloys; FePtMnSi displays larger Seebeck coefficients and power-factor tendencies, while CoPtMnAl exhibits higher electrical conductivity along with increased electronic thermal conductivity. Overall, these results highlight CoPtMnAl and FePtMnSi as promising candidates for spintronic applications.