Magnetoelastic fingerprints of metamagnetism in FeRh

Magnetic materials that undergo transitions between antiferromagnetic and ferromagnetic states are of considerable interest for fundamental physics and technological applications. The iron-rhodium alloy FeRh is a prominent example, yet several of its basic magnetic properties are not fully understood. Here, we show that the magnetocrystalline anisotropy and magnetoelastic response of FeRh differ substantially between its antiferromagnetic and ferromagnetic phases. Using first-principles calculations, we identify both qualitative and quantitative changes in these properties at zero temperature. We then develop a magnetic interatomic potential for atomistic spin-lattice simulations that reproduces the magnetoelastic behaviour obtained from the first-principles calculations. These results clarify the magnetoelastic coupling underlying metamagnetism in FeRh and establish a framework for large-scale simulations of materials exhibiting first-order antiferromagnetic-ferromagnetic phase transitions. Understanding how magnetic phases couple with lattice strains is key to developing advanced magnetocaloric devices. By modeling iron-rhodium, the authors show that a fundamental sign reversal in its magnetoelastic constants across the transition highlights the crucial interplay between its magnetic and structural properties.