Large nonreciprocity of shear-horizontal surface acoustic waves induced by a magnetoelastic bilayer

We report large nonreciprocity in the transmission of shear-horizontal surface acoustic waves (SHSAWs) on LiTaO₃ substrate coated with a Fe-Co-Si-B/Ni-Fe-Cu magnetoelastic bilayer. The large difference in saturation magnetization of the two layers not only brings nonreciprocal spin waves (SWs), but also ensures the phonon-magnon (SAW-SW) coupling at relatively low wave numbers. It is found that the angle between the static magnetization and the spin-wave vector plays a significant role in determining the strength of magnetoelastic coupling and nonreciprocity, simultaneously. A large nonreciprocal transmission of SAWs about 30 dB (i.e., 60 dB/mm) is demonstrated at 2.33 GHz. In addition, the dispersion relation between coupled SHSAWs and nonreciprocal SWs is developed, which provide a good insight into the observed phenomena. Our results offer a convenient approach to implement nonreciprocal SAW isolators or circulators.