Instability of the rhodium magnetic moment as the origin of the metamagnetic phase transition in α-FeRh

Based on ab initio total energy calculations we show that two magnetic states of rhodium atoms together with competing ferromagnetic and antiferromagnetic exchange interactions are responsible for a temperature-induced metamagnetic phase transition, which is experimentally observed for stoichiometric $\ensuremath{\alpha}\ensuremath{-}\mathrm{FeRh}.$ Taking into account the results of previous and newly performed first-principles calculations we present a spin-based model, which allows us to reproduce this first-order metamagnetic transition by means of Monte Carlo simulations. Further inclusion of spacial variation of exchange parameters leads to a realistic description of the experimental magnetovolume effects in $\ensuremath{\alpha}\ensuremath{-}\mathrm{FeRh}.$