Mechanically robust and thermodynamically stable FeSc₂Z₄ (Z = S, Se) spinels for future spintronic architectures

Spintronics, an emerging paradigm in next-generation electronics, fundamentally relies on materials that exhibit spin polarization, often achieved through intrinsic magnetic ordering in semiconductors as well as in metals. In this paper, the structural, mechanical, electronic, and thermodynamic characteristics of FeSc₂Z₄ (Z = S, Se) spinel compounds are systematically investigated using the density functional theory-based WIEN2k code. The calculated lattice constants are found to be 10.35 Å for FeSc₂S₄ and 10.83 Å for FeSc₂Se₄, comparable to the experimental lattice constants. Negative formation enthalpies of -1.67 eV (FeSc₂S₄) and -1.13 eV (FeSc₂Se₄) confirm that FeSc₂S₄ exhibits comparatively higher thermodynamic stability. Additionally, positive values of phonon frequency indicate both spinels are structurally stable. Elastic properties reveal mechanical robustness and ductility, as reflected by Poisson ratios of 0.31 and 0.32, and B ₀/G ratios of 2.31 and 2.44, respectively. However, electronic properties reveal that with increasing pressure from 0 to 4 GPa, both FeSc₂S₄ and FeSc₂Se₄ exhibit a monotonic reduction in their direct band gaps, with FeSc₂S₄ undergoing a transition to a half-metallic ferromagnetic state at higher pressures. Magnetic analysis yields a total magnetic moment of 4.00μ _B per formula unit in both materials, primarily originating from the Fe-site, indicating ferrimagnetic behavior. Furthermore, the values of entropy and Debye temperature using the quasi-harmonic Debye model-based GIBBS2 framework reflect the phonon softening, lattice stiffening, and anharmonic effects. These thermodynamic insights further support the thermal stability and vibrational integrity of FeSc₂Z₄ (Z = S, Se) spinels, underscoring their potential for spintronic and magneto-electronic device applications.