First-principles study of ferromagnetism and thermoelectric aspects of Sr(Pr/Nd)2S4 spinel chalcogenides as promising aspirants for spintronic and energy applications.

This article investigates the rare-earth-doped spinel chalcogenides Sr(Pr/Nd)2S4 for spintronics and thermoelectric applications. Spin-dependent structure optimization reveals their stability in the ferromagnetic state. Tolerance factors, formation energies, ab initio molecular dynamics simulations, and phonon band structures are calculated to evaluate their structural and thermodynamic stability. The spin-polarization density calculations and band structure analysis show 100% spin polarization and a ferromagnetic semiconducting nature. The spin-↑ channel has band gaps of ∼1.75 and 0.70 eV, and the spin-↓ channel is insulating. The exchange energies (Δx(f), Δx(pf)) and exchange constants (Noα, Noβ) are measured based on the strong coupling between the 4f-state of Pr/Nd and 3p-orbitals of S, leading to the creation of localized magnetic moments and the emergence of intriguing magnetic phenomena. Additionally, analyzing the electrical conductivity, power factor, thermal conductivity, and Seebeck coefficient by means of the BoltzTrap code helps to assess their suitability for transport applications. Thermoelectric performance has been measured by the figure of merit values of 0.84 and 0.58 for SrPr2S4 and SrNd2S4, respectively. The substantial values of transport parameters make these materials an evolving class for Spin electronics and thermal energy harvesting systems.