Improved Isolation Ratio in MSSWs-Based Inline Interference Device Using Dipolar-Coupled SWs Across a Micro-Air Gap

Control of spin-wave (SW) propagation is demonstrated by introducing a micro-air gap into a nanometer-thick yttrium iron garnet (Y₃Fe₅O₁₂, YIG) microstructure. SWs traverse the gap with reduced intensity following an exponential–linear decay with air gap length, attributed to coupling between incident and reflected dipolar SWs via a time-varying stray magnetic field. By tuning gap length, SW intensity is balanced to address nonreciprocity in counterpropagating magnetostatic surface SWs within an inline interference device. Introducing asymmetric gaps equalizes signal amplitudes and enhances the isolation ratio from 16 to 50 dB, the highest reported for such devices. This approach is applicable to SW-based logic gates and magnetic sensors, with the steep interference profile enabling high sensitivity at room temperature. The air gap also modifies SW transport properties, doubling group velocity from ≈2 km s⁻¹ in the reference device to 4.4 km s⁻¹ for a 66 µm gap at 22 mT, and inducing phase shifts of up to ≈37° for a 1 µm gap change (2–3 µm). These results establish a practical route to high-isolation magnonic interference devices and provide tunable control of group velocity and phase, enabling reconfigurable components such as delay lines and microwave phase shifters.