Spatiotemporal modulation of the magnetic order in FeRh using sub-gigahertz strain waves

We probe the first-order hysteretic antiferromagnetic (AFM) to ferromagnetic (FM) phase transition of FeRh in a FeRh/Ta/GaAs stack using surface acoustic waves (SAW) of three different frequencies up to 889 MHz. A clear signature of the phase transition is observed in the Rayleigh velocity and attenuation variations across the phase coexistence temperature range. The velocity variation closely follows the thermal hysteresis exhibited by the phase transition when probed with magnetometry, thereby enabling the determination of the FM fraction of FeRh versus temperature in the SAW path. The variation of attenuation is modeled under the assumption of strain-induced modulation of magnetic order via the movement of AFM-FM phase domain walls (PDWs) at the SAW frequency. This movement is driven by the strain-dependent difference between the AFM and FM Gibbs free energies, which originates from volume magnetostriction. The measured attenuation and its dependence upon the temperature and SAW frequency can be explained through a dissipative mechanism associated with the PDW oscillation driven by the strain wave. Finally, we demonstrate the drastic changes in the temperature dependence of SAW attenuation caused by the applied magnetic field within the FM-rich phase coexistence range, which arise from SAW-induced ferromagnetic resonance.