Multifunctional properties of manganese pnictides: A first-principles study on magneto-optics and magnetocaloric properties

Magnetic refrigeration presents an energy-efficient and environmentally benign alternative to traditional vapor-compression cooling technologies. It relies on the magnetocaloric effect, in which the temperature of a magnetic material changes in response to variations in the applied magnetic field. Optimal magnetocaloric materials are characterized by a significant change in magnetic entropy under moderate magnetic fields. In this study, we systematically investigated the interatomic exchange interactions, magnetic anisotropy energy and magnetocaloric properties of MnX (X=N, P, As, Sb, Bi) using a combination of density functional theory and Monte Carlo simulations. Additionally, the magneto-optical Kerr and Faraday spectra were computed using the all-electron, fully relativistic, full-potential linearized muffin-tin orbital method. The large magneto-optical response observed in MnBi originates from the interplay between the strong exchange splitting of Mn $3d$ states and the substantial spin-orbit interaction associated with the heavy Bi atom. To extract the site-projected spin and orbital moments, spin-orbit coupling and orbital polarization correction were accounted for in the present calculation, which shows good agreement between the moments obtained from the x-ray magnetic circular dichroism sum rule analysis, spin-polarized calculation, and experimental studies. The magnetic transition temperatures predicted through Monte Carlo simulations were in good agreement with the corresponding experimental values. Our results provide a unified microscopic understanding of magnetocaloric performance and magneto-optical activity in Mn-based pnictides and establish a reliable computational framework for designing next-generation magnetic refrigeration materials.