Structural, electronic, magnetic, optical, and thermoelectric properties of FeCrVAl and MnCrVAl quaternary Heusler alloys for spintronics and energy harvesting applications

A detailed first-principles study is carried out to explore the structural, elastic, electronic, magnetic, optical, and thermoelectric characteristics of the quaternary Heusler alloys FeCrVAl and MnCrVAl. The calculations are performed within the framework of density functional theory using the full-potential linearized augmented plane wave (FP-LAPW) method as implemented in the WIEN2k package, in conjunction with semi-classical Boltzmann transport theory via the BoltzTraP2 code. Structural optimization indicates that the Type-1 atomic arrangement represents the most energetically favorable configuration for both alloys. The computed elastic properties confirm excellent mechanical robustness, with FeCrVAl exhibiting bulk, shear, and Young’s moduli of 212.29 GPa, 130.66 GPa, and 325.24 GPa, respectively, while MnCrVAl shows corresponding values of 205.87 GPa, 136.75 GPa, and 266.31 GPa. The calculated Pugh ratios (1.63 for FeCrVAl and 1.50 for MnCrVAl) suggest a ductile mechanical response in both systems.Electronic structure calculations employing both GGA and mBJ-GGA functionals reveal half-metallic behavior with a minority-spin pseudogap near the Fermi level. Within the mBJ-GGA approach, the pseudogap widths are found to be approximately 0.3–0.4 eV for FeCrVAl and 0.4–0.5 eV for MnCrVAl. The total magnetic moments are calculated to be 2.00 µB/f.u. for FeCrVAl and 3.00 µB/f.u. for MnCrVAl, consistent with half-metallic ferromagnetism. Optical property analysis reveals large static dielectric constants and pronounced spin-dependent refractive indices, with ε₁(0) = 122 and n(0) = 11.1 for the spin-up channel of FeCrVAl, and ε₁(0) = 37 and n(0) = 6.0 for MnCrVAl, highlighting their possible relevance for magneto-optical applications. spin-dependent Seebeck coefficients and electrical conductivities, with FeCrVAl achieving σ/τ = 2.86 × 10²⁰ Ω⁻¹ m⁻¹ s⁻¹ at 300 K. After estimating the lattice thermal conductivity using the quasi-harmonic Debye/Slack approach, the estimated ZT values at 300 K are found to be low, namely 0.00104 for FeCrVAl and 0.00117 for MnCrVAl, indicating limited conventional thermoelectric power-generation performance. Overall, the coexistence of half-metallic ferromagnetism, mechanical stability, and spin-dependent thermoelectric response identifies FeCrVAl and MnCrVAl as attractive candidates for advanced spintronic and spin-caloritronic technologies.