🔬 materials science

Magnonic Fabry-Pérot resonators as programmable phase shifters

This paper demonstrates that magnonic Fabry-Pérot resonators, composed of a YIG film coupled with a CoFeB nanostripe, function as programmable phase shifters capable of inducing a controllable $\pi$ phase shift in spin waves through magnetic switching, thereby offering a promising low-loss component for reconfigurable spin-wave computing circuits.

Original authors: Anton Lutsenko, Kevin G. Fripp, Lukáš Flajšman, Andrey V. Shytov, Volodymyr V. Kruglyak, Sebastiaan van Dijken

Published 2026-10-21

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CC BY 4.0

Original authors: Anton Lutsenko, Kevin G. Fripp, Lukáš Flajšman, Andrey V. Shytov, Volodymyr V. Kruglyak, Sebastiaan van Dijken

Original paper licensed under CC BY 4.0 (http://creativecommons.org/licenses/by/4.0/). ✨ This is an AI-generated explanation of the paper below. It is not written or endorsed by the authors. For technical accuracy, refer to the original paper. Read full disclaimer

In the quest to make computers faster and more energy-efficient, scientists are looking beyond the flow of electricity to the behavior of magnetism itself. Inside magnetic materials, tiny waves called spin waves can carry information, much like ripples moving across a pond. These waves have two main properties that can be used to store data: how strong they are, known as amplitude, and where they are in their cycle of movement, known as phase. While controlling the strength of a wave is relatively straightforward, manipulating its phase is far more difficult yet essential for advanced computing tasks, such as performing logic operations where the timing of the wave determines the result. To build the next generation of computing devices, researchers need a way to precisely adjust this phase, ideally by flipping it completely, without losing the strength of the signal or requiring massive amounts of power.

A team of researchers has now demonstrated a new device that acts as a programmable switch for these magnetic waves. They created a tiny structure made from a thin film of a magnetic material called yttrium iron garnet, topped with a narrow stripe of a different magnetic alloy. When a spin wave travels through this setup, it encounters a special region where the two magnetic layers interact. This interaction causes the wave to change its wavelength, effectively squeezing it into a smaller space, and creates a cavity where the wave bounces back and forth between the edges of the stripe. By simply changing the direction of the magnetic field applied to the device, the researchers could switch the internal alignment of the magnets. This switch altered how the wave behaved inside the cavity, allowing them to flip the phase of the wave that emerged on the other side by exactly half a cycle, or 180 degrees, while keeping the wave's strength nearly the same.

The experiment took place in a laboratory setting where the team built a sample consisting of an 85-nanometer-thick film of yttrium iron garnet grown on a crystal base, with a 30-nanometer-thick stripe of cobalt-iron-boron alloy patterned on top. This stripe was 850 nanometers wide and 10 micrometers long, a size small enough to fit thousands of times across the width of a human hair. To test the device, they generated spin waves in the film using a microwave antenna positioned 20 micrometers away. They then used a specialized microscope that detects magnetic fields with extreme precision to watch how the waves moved through the stripe and what happened when they came out the other side. The microscope allowed them to see the waves in real space, capturing both their height and their timing as they traveled.

When the researchers applied a magnetic field, they observed that the device created a specific range of frequencies where the waves struggled to pass through, creating a gap in the transmission. Within this gap, the behavior of the waves depended entirely on how the magnets inside the stripe and the film were aligned relative to each other. If the magnets pointed in the same direction, the waves behaved one way; if they pointed in opposite directions, the waves behaved differently. The team found that by flipping the magnetic field, they could toggle between these two states. In one specific frequency range around 1.2 gigahertz, this toggle caused the wave emerging from the device to shift its phase by exactly half a cycle. Crucially, this shift happened without significantly weakening the wave, meaning the information it carried remained strong enough to be detected and used.

To confirm these observations, the researchers also ran detailed computer simulations that modeled the magnetic interactions at the atomic level. These simulations matched the experimental data almost perfectly, showing that the phase shift was a direct result of the changing magnetic alignment within the tiny stripe. The study revealed that the device could act as a programmable phase shifter, a component that can be turned on or off to change the timing of a signal on demand. This capability is vital for future computing architectures that rely on wave interference to perform calculations, as it allows for the creation of logic gates that can be reconfigured instantly. The ability to achieve such a precise phase shift over a distance of less than a micrometer suggests that these devices could be scaled down to fit into dense, complex circuits, offering a path toward more efficient and powerful information processing systems.

Technical Summary: Magnonic Fabry-Pérot Resonators as Programmable Phase Shifters

Problem Statement
Magnonics offers a pathway to improve data processing through enhanced energy efficiency and speed by encoding information in the amplitude or phase of spin waves. A critical component for phase-based information processing, such as in spin-wave majority gates, is a programmable phase shifter capable of modifying the phase of propagating spin waves on demand. While various tunable phase shifters exist (e.g., those based on domain walls, Oersted fields, or nonlinear effects), there is a need for scalable, low-power devices that can achieve significant phase modulation over short distances. Specifically, the ability to switch the phase by $\pi$ on demand is a desirable feature for wave-based computing architectures.

Methodology
The authors investigated a magnonic Fabry-Pérot resonator composed of a low-loss yttrium iron garnet (YIG) film coupled with a magnetic cobalt-iron-boron (CoFeB) nanostripe. The device operates via dynamic dipolar coupling, which facilitates nonreciprocal wavelength downconversion and the formation of a magnonic cavity.

Sample Fabrication: An 85-nm-thick YIG film was grown on a GGG substrate via pulsed laser deposition and annealed. A 30-nm-thick, 850-nm-wide, and 10- $\mu$ m-long CoFeB nanostripe was patterned on top, separated from the YIG by a 1-nm Ta/3-nm TaO $_x$ spacer.
Experimental Setup: Spin waves were excited in the YIG film using a microwave antenna positioned 20 $\mu$ m from the resonator. A magnetic bias field was applied parallel to the antenna to excite Damon-Eshbach spin waves.
Characterization: The team utilized super-Nyquist sampling magneto-optical Kerr effect (SNS-MOKE) microscopy to measure the amplitude and phase of transmitted spin waves. Scans were performed along a line crossing the resonator center and a parallel reference line.
Simulations: Micromagnetic simulations were conducted using MuMax3 software to complement experimental data, modeling the specific material parameters of the YIG and CoFeB layers and the geometry of the excitation antenna.

Key Contributions and Results
The study demonstrates that magnonic Fabry-Pérot resonators can function as programmable phase shifters capable of inducing a $\pi$ phase shift in transmitted spin waves.

Resonance and Magnetization States: Transmission spectra revealed distinct gaps corresponding to the $n=2$ Fabry-Pérot resonance. The frequency of these gaps shifts abruptly as the magnetic field is swept, corresponding to transitions between parallel and antiparallel magnetization configurations of the YIG film and CoFeB nanostripe. This results in four distinct "magnonic states" due to the system's chirality.
Wavelength Conversion and Phase Accumulation: Upon entering the resonator, incident spin waves with wavelength $\lambda_1$ undergo downconversion to shorter wavelengths ( $\lambda_2$ or $\lambda_3$ ) depending on the magnetization alignment. This significant wavelength reduction allows for the accumulation of a substantial phase shift over the short 850-nm width of the resonator.
Programmable $\pi$ Phase Shift: The most significant finding is the ability to switch the phase of the transmitted spin wave by $\pi$ on demand. By reversing the magnetization of the CoFeB nanostripe (while maintaining the YIG magnetization along the positive y-direction), the phase shift changes from approximately 0 to $\pi$ (or vice versa) within the 1.1–1.3 GHz frequency range.
Amplitude Preservation: At a specific frequency of approximately 1.2 GHz, the resonator induces a $\pi$ phase shift while maintaining a consistent transmission amplitude (reduced to ~65% of the input) for both parallel and antiparallel states. This confirms the device's capability to perform phase inversion without significantly altering signal magnitude.
Wavefront Deformation: SNS-MOKE imaging showed that the resonator induces a phase shift that curves the spin-wave wavefronts, creating caustic beams emanating from the nanostripe edges. This curvature is a direct manifestation of the accumulated phase shift over the resonator's width.

Significance
The paper posits that the magnonic Fabry-Pérot resonator is a promising component for reconfigurable magnonic circuits and spin-wave computing devices. Its ability to provide a controllable $\pi$ phase shift over a nanoscale distance (850 nm) addresses the scalability requirements for integrating phase-shifting elements into magnonic logic gates. The device operates with low-loss transmission and allows for on-demand control via magnetic switching, fulfilling key criteria for efficient phase-based information processing. The authors conclude that this functionality positions the resonator as a viable solution for advanced data processing architectures where programmable phase shifting is essential.

Technical Summary: Magnonic Fabry-Pérot Resonators as Programmable Phase Shifters

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