Spin-wave reservoir chips with short-term memory for high-speed estimation of external magnetic fields

The experimental realization of a spin-wave reservoir chip employing ferromagnetic permalloy thin films is presented. The novel device facilitates the interference of three spherical wave-excited surface mode spin waves within a rectangular waveguide via strategically positioned slits, enabling the detection of electrical signals from surface mode spin waves across all four observation antennas. Through the experiments conducted, it is confirmed that the device functions as a one-input, four-output reservoir capable of estimating external magnetic fields. Notably, the results demonstrate the device's capacity to retain memory up to one step prior in short-term memory tasks, while confirming the effectiveness of spinwave interference induced by Huygens slits in enhancing nonlinearity, as observed in parity-check tasks. Furthermore, the inclusion of additional detection antennas contributes to improved learning accuracy, highlighting the significant progress achieved by the spin-wave reservoir chip. These findings underscore substantial progress toward practical implementation, with promising avenues for further development and refinement, showing its remarkable ability to process signals at high speeds, even with 0.8-ns pulse sequences.