Strong coupling between spin waves and surface acoustic waves*

Hybridized states are characteristic of the strong coupling regime where the coupling strength is higher than the relaxation rates of each independent state. This condition ensures the coupled system exhibits coherent behavior, enabling efficient energy transfer. Several research reported realizations of strong magnon–phonon coupling, however, the strong dependence of the phonon wavelength on the dimensionality of the active magnetic layer within the structure imposes limitations on the separate control of the phonon wavelength and the size of the magnet, hindering the potential to enhance the coupling strength by increasing the volume of the magnet. In response to this challenge, we adopted an on-chip surface acoustic wave (SAW) resonator containing a thin ferromagnetic film enabling the systematic adjustment of the magnet's size while maintaining a consistent phonon wavelength. Here we present the experimental realization of strong coupling between magnons and SAW phonons by analyzing dispersion anticrossings. We detect a monotonic increase in the coupling strength by expanding the ferromagnetic film thickness, which agrees with our expectation. Our work provides a significant way to advance fundamental research and develop devices based on magnon–phonon hybrid quasiparticles.