🔬 mesoscale physics

Spin-Wave Phase Shifter Controlled by a Domain Wall Racetrack

This paper proposes and demonstrates via micromagnetic simulations a compact, programmable spin-wave phase shifter that utilizes the stray field from a moving domain-wall racetrack to modulate the phase of Damon-Eshbach spin waves in an underlying YIG film, offering a promising route for interference-based magnonic circuits and in-memory computing.

Original authors: Uladzislau Makartsou, Olena Tartakivska, Paweł Gruszecki, Anton Lutsenko, Sebastiaan van Dijken, Volodymyr V. Kruglyak, Maciej Krawczyk

Published 2026-06-17

📖 4 min read☕ Coffee break read

CC BY 4.0

Original authors: Uladzislau Makartsou, Olena Tartakivska, Paweł Gruszecki, Anton Lutsenko, Sebastiaan van Dijken, Volodymyr V. Kruglyak, Maciej Krawczyk

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

Imagine you are trying to send a message using ripples on a pond. In the world of advanced computing, scientists are trying to do something similar, but instead of water, they use spin waves—tiny ripples of magnetic energy that travel through special materials. These waves can carry information, not by how big the ripple is (amplitude), but by when the ripple peaks (phase).

To process this information, you need a way to control the timing of these ripples. If you want two ripples to crash into each other and make a bigger wave, or cancel each other out to make silence, you need to be able to shift their timing precisely. This is where the "phase shifter" comes in.

The Problem: How to Shift the Timing?

Usually, to change the timing of a wave, you might change the shape of the path it travels (like making a road longer or shorter). But in tiny computer chips, you can't keep rebuilding the roads every time you want to send a new message. You need a switch that can change the timing without changing the physical shape of the device.

The Solution: A Magnetic "Traffic Controller"

The researchers in this paper propose a clever solution using a Domain Wall Racetrack.

Think of the racetrack as a narrow, magnetic highway made of a material called Permalloy, sitting just above a "pond" made of YIG (a magnetic crystal).

The Racetrack: This highway has little notches (bumps) in it that act like parking spots.
The Domain Walls: These are like invisible walls of magnetic energy that can be parked in those spots.
The Magic: When these magnetic walls are parked in specific spots, they create a "ghost field" (a stray magnetic field) that reaches down into the YIG pond below.

How It Works: The Invisible Hand

Imagine the spin waves are swimmers trying to cross the pond.

No Walls Parked: If the magnetic highway is empty or uniform, the swimmers cross at a normal speed.
Walls Parked: When the researchers park the magnetic walls in specific configurations (called "010" or "101"), the "ghost field" from the walls acts like an invisible hand.
- In one configuration, the hand pushes the swimmers, making them move slightly faster.
- In the opposite configuration, the hand pulls them back, making them move slightly slower.

Because the swimmers move at different speeds for a short distance, they arrive on the other side at a different time. This change in arrival time is the phase shift.

The Results: A Precise Switch

The paper shows that by simply moving these magnetic walls to different parking spots using an electric current (without changing the physical shape of the chip), they can shift the timing of the waves by up to 90 degrees.

This is a huge shift, enough to completely flip the logic of the signal (turning a "yes" into a "no" or vice versa).
Crucially, the strength of the wave doesn't get weaker; it just changes its timing.
The researchers tested this with computer simulations and found that a simple mathematical model (like a rule of thumb for waves) perfectly predicted how the magnetic walls would change the wave's timing.

Why It Matters

This device is like a programmable traffic light for magnetic waves. Instead of building a new road for every new traffic pattern, you just flip a switch to change the timing.

The authors suggest this could be a key building block for:

New Types of Computers: Machines that use wave interference (like the ripples crashing together) to do calculations, which could be much more efficient than today's computers.
In-Memory Computing: Since the magnetic walls stay in their parked position even when the power is turned off (non-volatile), this device could act as both a memory storage unit and a processor at the same time.

In short, the paper demonstrates a way to control the "rhythm" of magnetic waves using a tiny, movable magnetic switch, paving the way for a new generation of compact, efficient computers.

Technical Summary: Spin-Wave Phase Shifter Controlled by a Domain Wall Racetrack

Problem and Motivation
The development of magnonic circuits for information processing relies heavily on the ability to control the phase of propagating spin waves (SWs). SW interference is a fundamental mechanism for logic operations, pattern recognition, and neuromorphic computing, where the relative phase of input signals determines output states. While various approaches exist for SW phase manipulation—ranging from resonant coupling in Fabry–Pérot cavities to non-resonant methods involving graded magnonic indices—there is a need for compact, programmable, and non-volatile phase shifters that can be integrated into existing memory architectures. Specifically, the authors aim to bridge the gap between magnetic domain-wall (DW) racetrack memory and magnonic logic by utilizing the stray fields of DWs to locally modulate SW properties without altering the waveguide geometry.

Methodology
The study employs micromagnetic simulations using the MuMax3 software to model a hybrid system consisting of a Permalloy (Py) domain-wall racetrack placed 5 nm above a 50 nm thick Yttrium Iron Garnet (YIG) film.

Geometry: The Py racetrack is 50 nm wide and 20 nm thick, featuring two triangular notches (21 nm side length) separated by 320 nm to pin domain walls. The YIG film is biased by a static external magnetic field ( $B_{ext} = -15$ mT) along the z-axis, ensuring saturation while maintaining DW stability.
Excitation: Monochromatic Damon–Eshbach (DE) spin waves are excited in the YIG film and propagate along the x-axis, passing beneath the racetrack.
Configurations: The study compares four magnetic states of the racetrack: two uniform states (000 and 111, representing parallel and antiparallel magnetization relative to YIG) and two multi-domain states (010 and 101) containing two pinned DWs with opposite magnetic charges.
Analysis: The authors evaluate the accumulated phase shift ( $\Delta\phi$ ) and transmission attenuation across a frequency range of 2.5–5.0 GHz. They also develop a semi-analytical model based on the Wentzel–Kramers–Brillouin (WKB) approximation to correlate the observed phase shifts with the stray field-induced modifications of the effective magnetic field.

Key Results

Phase Control via Domain Walls: The presence of domain walls in the racetrack induces significant phase shifts in the underlying YIG film. The two multi-domain configurations (010 and 101) produce phase shifts of opposite signs, ranging from approximately $+71^\circ$ to $-84^\circ$ across the 2.5–5.0 GHz band. In contrast, the uniform racetrack configurations (000 and 111) exhibit negligible phase shifts (less than $5^\circ$ ) for widths $\le 80$ nm, confirming that the effect is driven by the DWs rather than the uniform Py layer.
Mechanism: The phase shift is attributed to the stray magnetic field generated by the volume magnetic charges at the DWs. This field locally modifies the effective magnetic field ( $B_{eff,z}$ ) in the YIG film, thereby altering the local SW wavelength and the accumulated phase. The 010 configuration increases the effective field modulus (slowing phase variation), while the 101 configuration decreases it (accelerating phase variation).
Amplitude Preservation: The device operates with minimal signal loss. The transmitted SW intensity remains close to the reference level (attenuation $< 1$ dB) for the DW configurations, indicating that the phase shifting mechanism does not significantly dampen the wave.
Model Validation: The semi-analytical WKB model, which integrates the position-dependent wave number derived from the simulated effective field profiles, shows strong agreement with the full micromagnetic simulations. This confirms that the phase shift is dominated by the DW-induced stray field and the resulting change in the dispersion relation.
Robustness in Open Geometries: The phase-shifting effect persists even when the SWs are not confined to a narrow channel by absorbing boundary conditions but are allowed to diffract through a single aperture. While the beam shape changes slightly depending on the magnetic configuration, the phase shift magnitude remains comparable to the confined case.

Significance and Claims
The paper claims to demonstrate a route toward a compact, programmable spin-wave phase shifter suitable for interference-based magnonic circuits. By integrating a magnetic DW racetrack with a YIG waveguide, the device offers a non-volatile method to control SW phase without modifying the physical waveguide geometry. The authors suggest that this approach could facilitate the integration of non-volatile memory functions with unconventional magnonic computing architectures, such as neuromorphic networks and reservoir computing, where phase-encoded information is processed via interference. The ability to achieve phase shifts of up to $\pm 90^\circ$ with high transmission efficiency and scalability via current-driven DW displacement positions this concept as a potential functional element for future magnonic information processing systems.

The Problem: How to Shift the Timing?

The Solution: A Magnetic "Traffic Controller"

How It Works: The Invisible Hand

The Results: A Precise Switch

Why It Matters

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