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 $C_{11}$ constant is noticeably larger in the FM phase than in the AF phase, while $C_{12}$ and $C_{44}$ 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 machine-learned 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 temperature- and 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.