The magnetic, electronic, elastic, and optical properties of the double perovskite Cs₂KGdCl₆

Cesium-based double halide perovskites have gained attention as environmentally benign, lead-free candidates for next-generation spintronic and optoelectronic applications. In this work, we employ first-principles density-functional theory, using the full-potential linearized augmented plane-wave (FP-LAPW) method within the Generalized Gradient Approximation of Perdew–Burke–Ernzerhof (GGA-PBE), to investigate the structural, magnetic, elastic, electronic and optical properties of the double perovskite Cs 2 KGdCl 6 . Our results confirm a stable cubic crystal structure, mechanical robustness and moderate ductility, with a notable Zener anisotropy factor indicating directional dependence of its elastic behavior. The magnetic ground state, predominantly influenced by Gd[Formula: see text] ions, favors ferromagnetic ordering at low temperatures. Electronic-structure calculations reveal spin-polarized band gaps and highlight the crucial role of Gd 4f and Cl 3p states near the Fermi level, offering insights into potential spin-filter mechanisms. Optical analysis shows transparency in the visible range, together with pronounced absorption and plasmonic features in the ultraviolet regime. Taken together, these findings present Cs 2 KGdCl 6 as a versatile, stable and tunable material platform, bridging fundamental research and technological applications in spintronics, optoelectronics and beyond.