Giant Non-reciprocity Driven by Strong Magnon-Phonon Coupling in Low-Loss Fundamental Mode Magnetoacoustic RF Devices

Integrated nonreciprocal isolators and circulators have transformed wireless communication but are power-hungry (40mW~200mW), limiting their use in low-power applications. Recently, magnetoacoustic non-reciprocal RF devices have demonstrated substantial nonreciprocity with impressive power efficiency for low-power, wideband full-duplex wireless systems. These devices consist of a magnetic stack within the surface acoustic wave (SAW) path between two interdigital transducers (IDTs) on a piezoelectric substrate. RF voltage on the IDTs generates a SAW that interacts with non-recirprocal spin wave (SW) in the magnetic stack. Strong magnon-phonon coupling leads to hybrid magnetoacoustic waves exhibiting a much higher backward loss rate than the forward one or vice versa. Ongoing research strives to enhance non-reciprocity strength and bandwidth while maintaining high transmission between device ports. Despite successful demonstrations of non-reciprocity in magnetic stacks such as FeGaB/Al₂O₃/FeGaB, the insertion loss is still high (>50 dB) owing to high-order mode SAW harmonics. Here we demonstrated a low-loss magnetoacoustic non-reciprocal RF device driven by SAW fundamental mode at 2.87 GHz. In our devices, a low insertion loss of only 10-dB and a sharp acoustic resonance lead to strong magnon-phonon coupling. The consequent giant non-reciprocity of 200 dB/mm make the device a potential candidate for integrated compact, power-efficient RF isolators and circulators.