Enhancement of spin-wave nonreciprocity and group velocity in a low-wavenumber regime (2509.04806v1)

Abstract: Nonreciprocity of spin waves is essential for components such as magnetic isolators and circulators used in spin-wave-based computing. A ferromagnetic (FM) bilayer exhibits significant frequency nonreciprocity and has attracted attention in recent years. Prior research on bilayers has predominantly focused on the high-wavenumber regime, where spin waves display significant nonreciprocity and are accessible through Brillouin light scattering (BLS). However, the dynamics at low wavenumbers (k < 5 rad/um), which enable rapid magnon propagation, have yet to be thoroughly investigated. We investigate spin-wave propagation in the bilayer using coplanar waveguides (CPWs) and demonstrate that increasing the bilayer thickness enhances nonreciprocity even at low wavenumbers, which leads to the high group velocity originating from the Damon-Eshbach (DE) mode. These findings establish design principles for high-speed, low-loss spin-wave-based information processing.