First-principle study of Mg-based rare earth spinels MgSm2Y4 (Y[dbnd]S, Se) for spintronic and thermoelectric devices

Abstract

Mechanical, spin-polarized electronic, and transport characteristics of rare-earth-based MgSm2Y4 (YS, Se) spinels are investigated using first-principle calculations. In contrast to the anti-ferromagnetic and nonmagnetic states of MgSm2Y4 (YS, Se), the optimization study reveals that ferromagnetic states release more energy, and optimized lattice constants in ferromagnetic states are comparable to existing values. Phonon dispersion and formation energy are also calculated to confirm the dynamical stability stability. The ductile character is confirmed by investigating the Poisson's and Pugh ratios, and the values of other elastic parameters show their importance for the manufacturing of devices. Heisenberg model and the density of electron states at the Fermi level report the Curie temperature and the spin polarization. Spin-polarized electronic properties indicate half-metallic ferromagnetic because the spin-down reflects a semiconductor nature, whereas the metallic nature manifests the spin-up. The total magnetic moments are generated through hybridization of chalcogenide 2p-states and the Sm f-states. We found that the studied spinels may be used in thermoelectric devices by examining transport characteristics such as electronic and phononic thermal conductivity, Seebeck co-efficient, and figures of merit (ZT). Our results indicate that the ZT for MgSm2S4 is almost three times the ZT obtained for MgSm2Se4.