Acoustoelectric nonlocal spin-wave-power detector for studying magnon-phonon coupling

We have developed a simple detection scheme to study spin waves excited by surface acoustic waves (SAWs) in ferromagnetic thin films. Metallic antennas made of $\mathrm{Ta}$ and a ferromagnetic element are placed along the SAW propagation path. The SAW excites spin waves in the ferromagnetic element and induces acoustoelectric current in the antennas: the latter is detected as a dc voltage. The dc voltage takes an extremum at the spin-wave resonance condition. The antennas placed before and after the ferromagnetic element along the SAW propagation path can probe spin-wave excitation from reflected and transmitted SAWs, respectively. Interestingly, we find characteristics of spin-wave excitations that are different for the reflected and transmitted SAWs: the former excites spin waves with larger frequency with broader linewidth compared to the latter. The results show that the antennas act as a nonlocal spin-wave-power detector and can be used to map out the spin-wave spectra in a unique way, providing insights into the magnon-phonon coupling in magnetic nanostructures fabricated on phononic SAW devices.