Experimental determination of the temperature- and phase-dependent elastic constants of FeRh

The elastic constants of an epitaxial film of FeRh have been determined experimentally in both ferromagnetic (FM) and antiferromagnetic (AF) phases, using a combination of Brillouin light scattering and picosecond acoustics experiments. The C11 constant is noticeably larger in the FM phase than in the AF phase, while C12 and C44 are both lower, leading to larger Rayleigh wave velocities in the FM phase than in the AF phase. The elastic constants were calculated numerically using first-principles anharmonic modeling and machinelearned interatomic potentials. We find that using a temperature-dependent effective potential is indispensable to correctly reproduce the experimental values to within 80-100%. The accurate knowledge of the temperatureand phase-dependences of the elastic constants of crystalline FeRh are valuable ingredients for the predictive modeling of the acoustic and magnetoacoustic properties of this magnetostrictive material.