Breakthrough in On-Chip Acoustic Isolation Using Magnetic Thin Films

Researchers have successfully demonstrated a method to create a one-way transmitter for surface acoustic waves (SAWs) by integrating a magnetic thin film onto a piezoelectric chip. This achievement, which transfers the intrinsic nonreciprocity of magnetism to sound waves, is a critical step toward more compact and efficient radio-frequency (RF) signal processing devices.

SAW filters are essential components in modern wireless electronics like smartphones. Their slow propagation speed allows for the design of exceptionally compact filters for microwave frequencies. A key challenge, however, has been achieving nonreciprocal or "one-way" acoustic transport, which would allow a single device to function as both a transmitter and a receiver without interference.

The international team, led by Prof. YoshiChika Otani and involving researchers from RIKEN, ISSP Tokyo, and the Spin Insulatronics group, addressed this by fabricating an on-chip device. They deposited a thin film of the ferrimagnetic insulator yttrium iron garnet (YIG) onto a piezoelectric substrate. YIG was chosen for its exceptionally low magnetic damping and long magnon (spin wave) lifetime. Using focused-ion-beam techniques, they created a device where SAWs generated by interdigitated transducers interact directly with the magnetic film.

The experiment revealed strong, resonant absorption of the SAWs by the YIG layer. Crucially, this absorption was nonreciprocal: it changed significantly when the direction of the SAW propagation was reversed. The team observed multiple absorption peaks corresponding to different perpendicular standing spin wave (PSSW) modes within the YIG film. Higher-order spin wave modes exhibited particularly pronounced nonreciprocal behavior.

These experimental results align with theoretical models that incorporate asymmetric surface conditions and the nonreciprocal nature of the coupling between magnons and phonons (sound particles). The work, detailed in the open-access paper *"Nonreciprocal Resonant Surface Acoustic Wave Absorption in Y₃Fe₅O₁₂"* (Physical Review B, 2025), establishes on-chip YIG-SAW devices as a versatile platform.

The strong and controllable nonreciprocal attenuation demonstrated here paves the way for highly efficient, integrated acoustic isolators and circulators. This advancement is significant for both applied RF engineering and fundamental research into magnon-phonon interactions and next-generation magnonic technologies.

*Funding was provided through the Q-SPIN chair of excellence LANEF.*

Magnetism is well-known to inherently break time-reversal symmetry; for example, the magnetization precesses in a single (counter-clockwise) direction around its equilibrium axis. By integrating a magnetic thin film onto a piezoelectric substrate, enabling phonons to hybridize with magnons, we show that this intrinsic nonreciprocity can be transferred to surface acoustic waves.

Surface acoustic wave (SAW) filter: Two interdigitated transducers (IDT1 and IDT2) generate elastic surface waves in a piezoelectric crystal, which then interact with a magnetic garnet thin film deposited on the same surface.

Surface acoustic wave (SAW) filters are at the forefront of modern wireless electronics. Their slow propagation speed (~1000 m/s) enables the design of compact filters for the microwave frequency range. Achieving one-way acoustic transport is crucial for using the same device as both a transmitter and a receiver. Here, we propose to realize this functionality by integrating a thin film of the ferrimagnetic insulator yttrium iron garnet (Y3Fe5O12, YIG) into the device, as illustrated in the figure. YIG is particularly attractive due to its low magnetic damping and long magnon relaxation time.

While magnetoelastic interactions between YIG and SAWs have been used to implement acoustic isolators, achieving on-chip SAW-driven magnetic resonance has been challenging due to material-device integration constraints. In this work, we demonstrate nonreciprocal resonant SAW absorption in an on-chip YIG-SAW device fabricated using focused-ion-beam techniques. Multiple absorption peaks are observed, corresponding to perpendicular standing spin wave (PSSW) modes, with higher-order PSSWs exhibiting pronounced nonreciprocity when the SAW propagation direction is reversed. These observations are consistent with theoretical models that account for asymmetric surface conditions and nonreciprocal magnon-SAW coupling.

The strong nonreciprocal SAW attenuation in YIG offers a promising pathway toward highly efficient RF signal processing. Our results establish on-chip YIG-SAW devices as a versatile platform for studying nonreciprocal SAW absorption, magnon-phonon interactions, and advanced YIG-based magnonic technologies.

Teams: Spin Insulatronics

Collaborations: RIKEN et ISSP Tokyo (JP)

Funding: Q-SPIN chaire d’excellence LANEF portée avec le Prof. YoshiChika Otani

Further reading: Nonreciprocal Resonant Surface Acoustic Wave Absorption in \({Y}{₃}{Fe}₅O₁₂\), Y. Ba, J. Puebla, K. Yamamoto, Y. Hwang, L. Liao, S. Maekawa, O. Klein, and Y. Otani, Physical Review B 111, 104401 (2025). Open access: cea-05003586v1

Contact: Olivier Klein

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