Frustrated magnetism and caloric effects in Mn-based antiperovskite nitrides: Ab initio theory

Abstract

We model changes of magnetic ordering in Mn-based antiperovskite nitrides driven by biaxial lattice strain at zero and at finite temperature. We employ a noncollinear spin-polarized density functional theory to compare the response of the geometrically frustrated exchange interactions to a tetragonal symmetry breaking (the so called piezomagnetic effect) across a range of ${\mathrm{Mn}}_{3}\mathrm{AN}$ (A = Rh, Pd, Ag, Co, Ni, Zn, Ga, In, Sn) at zero temperature. Building on the robustness of the effect we focus on ${\mathrm{Mn}}_{3}\mathrm{GaN}$ and extend our study to finite temperature using the disordered local moment (DLM) first-principles electronic structure theory to model the interplay between the ordering of Mn magnetic moments and itinerant electron states. We discover a rich temperature-strain magnetic phase diagram with two previously unreported phases stabilized by strains larger than 0.75% and with transition temperatures strongly dependent on strain. We propose an elastocaloric cooling cycle crossing two of the available phase transitions to achieve simultaneously a large isothermal entropy change (due to the first-order transition) and a large adiabatic temperature change (due to the second-order transition).