CsFeX ₃ (X = F, Cl, Br, I) for Spintronic and IR‐Region Optoelectronic Applications: First‐Principles Investigations

A comprehensive investigation on the structural, electronic, optical, mechanical, and thermodynamic properties of CsFeX ₃ (X = F, Cl, Br, I) using ab initio total energy calculations is performed. These cesium ferrous trihalides exhibit 100% spin polarization, with semiconducting spin‐up electrons and metallic spin‐down electrons. DFT + U calculations using varying strengths of the Coulomb interaction parameter confirm half‐metallic behavior with no band gap opening in the spin‐down band structures. These halides exhibit a strong infra‐red region absorption owing to the intraband d – d spin down electron level transitions of Fe and a high (>4) refractive index. Only CsFeCl ₃ and CsFeBr ₃ satisfy the Born criteria of mechanical stability. CsFeBr ₃ is more ductile, and CsFeCl ₃ has a smaller anisotropy in the Poisson’s ratio, shear, and Young’s modulus. CsFeCl ₃ is the most promising cesium ferrous trihalide for spintronic and IR‐region optoelectronic device applications, being half‐metallic with good optical, mechanical, and thermodynamic characteristics.