Nonlinearity Enhancement in Spin-Wave Reservoir Computing with the Utilization of Coexisting Magnetostatic Modes

We propose a novel spin-wave-based reservoir computing (RC) chip-and-antenna structure that utilizes two coexisting magnetostatic modes. In our structure, both backward volume spin waves (BVSW) and surface spin waves (SSW) simultaneously arise and propagate in a magnetic film, leading to enhanced nonlinearity. We name this type of setup multiple-mode coexisting (MMC) structures. First in numerical analysis of MMC structure, we examine the frequency spectrum of the output signals and quantify the degree of nonlinearity. We then perform a signal transformation task to evaluate the nonlinearity enhanced in our MMC structure. Our results show that the use of two modes significantly enhances the even and odd harmonics and achieves a high performance improvement index up to 25.4% compared to 5% in conventional single-mode cases. The results demonstrate the enhanced nonlinearity of the MMC structure, which is essential not only for improving the performance of spin-wave-based RC systems but also for enabling the practical implementation of spin-wave reservoir chips.