Harnessing the half-metallicity and thermoelectric insights in Cs2AgMBr6 (M = V, Mn, Ni) double halide perovskites: A DFT study

Herein, we undertake a detailed exploration of the structural stability, magneto-electronic behavior, and thermoelectric properties of Cs₂AgMBr₆ (M = V, Mn, Ni) halide double perovskites using first-principles approach. The study commences with a meticulous assessment of both structural stability and thermodynamic properties employing various metrics. Energy minimization across different phases, utilizing the Birch-Murnaghan equation of state, confirms the ferromagnetic phase as energetically favoured, supported by Curie-Weiss constants of 98 K, 100 K, and 150 K for V, Mn, and Ni-based perovskites, respectively. Mechanical properties, including hardness, stiffness, ductility, and fracture strength, are derived from the simulated elastic constants, ensuring the mechanical stability of the materials. Electronic structure analysis, performed using the PBE-GGA and GGA + mBJ functionals, reveals that Cs₂AgMBr₆ compounds exhibit half-metallic ferromagnetism, with 100 % spin polarization at the Fermi level. Analysis of the partial density of states highlights the half-metallic ferromagnetic mechanism, confirming predominant ferromagnetic order through parameters such as the exchange splitting energy (Δ_x), p-d exchange interaction energy (Δ_x(p-d)), crystal-field energy (E_crys), and exchange constants (N₀α and N₀β). The negative values of the exchange constants further validated the dominant ferromagnetic order in both s-d and p-d interactions, with unpaired electrons contributing magnetic moments of 2 μ_B for V, 4 μ_B for Mn, and 1 μ_B for Ni-based perovskites. Also, the Curie temperatures are calculated as 385 K, 747 K, and 204 K for V, Mn, and Ni-based perovskites. The overall findings, which reveal 100 % spin polarization and high zT values, underscore the significant potential of Cs₂AgMBr₆ halide perovskites for advancing spintronics and thermoelectric applications.