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

Abstract

We report large nonreciprocity in the transmission of shear-horizontal surface acoustic waves (SHSAWs) on ${\mathrm{Li}\mathrm{Ta}\mathrm{O}}_{3}$ substrate coated with a $\mathrm{Fe}\text{\ensuremath{-}}\mathrm{Co}\text{\ensuremath{-}}\mathrm{Si}\text{\ensuremath{-}}\mathrm{B}/\mathrm{Ni}\text{\ensuremath{-}}\mathrm{Fe}\text{\ensuremath{-}}\mathrm{Cu}$ 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.