Dynamic stability, half-metallicity, and optical properties of Fe2CrX (X = Si, Ge) full-heusler alloys: Competition between L21 and XA ordering

• Investigated structural, electronic, magnetic, and optical properties of Fe 2 CrSi and Fe 2 CrGe. • Fe 2 CrSi prefers L2 1 , while Fe 2 CrGe is stable in XA, confirmed via phonon and elastic analyses . • Half-metallic and half-semiconducting behaviors with magnetic moments up to 2 µ B identified. • Fe 2 CrGe shows enhanced absorption and conductivity, ideal for photovoltaic applications. • Fe 2 CrSi is suitable for UV-sensitive devices, while Fe 2 CrGe suits spintronic technologies. We performed spin-polarized density functional theory (DFT) studies on the structural, mechanical, dynamic, thermodynamic, electronic, magnetic, and optical properties of Fe 2 CrSi and Fe 2 CrGe full-Heusler alloys. Using GGA-PBE and mBJ-GGA, we found that Fe 2 CrSi is stable in the L 2 1 −type structure, while Fe 2 CrGe prefers the XA -type structure. Phonon calculations confirm the dynamic stability, while elastic constants indicate mechanical stability for Fe 2 CrGe in both structures. However, Fe 2 CrSi in L 2 1 does not satisfy the Born mechanical stability criteria due to a negative (C 11 − C 12 ) value, though its dynamic stability and negative formation energy suggest its potential experimental realizability. Electronic structure analysis shows half-metallic behavior with GGA-PBE and half-semiconducting gaps of 0.47 eV (Fe 2 CrSi) and 0.60 eV (Fe 2 CrGe) using mBJ-GGA. Fermi Surface analysis reveals distinct topologies and carrier distributions influencing electronic transport properties. Fe 2 CrSi exhibits a more symmetric and interconnected Fermi Surface, favoring high carrier mobility, whereas Fe 2 CrGe displays a fragmented topology, suggesting more localized states. Optical properties highlight Fe 2 CrGe’s superior absorption across the visible spectrum, making it suitable for photovoltaics, while Fe 2 CrSi exhibits strong UV absorption, promising for UV-sensitive devices. Additionally, Fe 2 CrGe shows higher optical conductivity, indicating potential in light-harvesting and optoelectronic applications. These findings highlight Fe 2 CrZ alloys as promising candidates for spintronics and optoelectronic applications.