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Plasmonic Metasurfaces for Magnetic Skyrmion Control via the Inverse Faraday Effect

This paper demonstrates a deterministic, ultrafast, all-optical method for writing and erasing magnetic skyrmions using a magneto-plasmonic metasurface that leverages the inverse Faraday effect to generate synchronized picosecond magnetic field pulses, thereby overcoming the stochastic limitations of thermal excitation for high-speed topological data storage.

Original authors: Xingyu Yang, Tristan da Câmara Santa Clara Gomes, Chantal Hareau, Ye Mou, Tingjun Zheng, Maria Sanz-Paz, Nicolas Reyren, Jack Gartside, Mathieu Mivelle

Published 2026-10-07

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CC BY 4.0

Original authors: Xingyu Yang, Tristan da Câmara Santa Clara Gomes, Chantal Hareau, Ye Mou, Tingjun Zheng, Maria Sanz-Paz, Nicolas Reyren, Jack Gartside, Mathieu Mivelle

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 build faster, smaller, and more efficient computers, scientists have long looked to the tiny magnetic swirls found within certain materials. These swirls, known as magnetic skyrmions, are stable, particle-like knots of magnetism that can be packed tightly together to store data. Because they are so small and require very little energy to move, they are considered ideal candidates for the next generation of memory devices and computing systems. However, a major hurdle has stood in the way of using them: while scientists can move these magnetic knots around, creating or destroying them on demand has been difficult. Existing methods often rely on heating the material, a process that is unpredictable and can damage the delicate structures. It is like trying to build a house of cards by blowing hot air; you might get the cards to move, but you cannot guarantee exactly where they will land or how to take them apart without knocking the whole thing over.

A team of researchers has now proposed a different way to handle these magnetic knots, one that avoids heat entirely and uses light instead. By combining a special pattern of silver disks with a magnetic film, they demonstrated a method to write, erase, and reshape these magnetic structures in mere trillionths of a second. The key to this process is a phenomenon called the inverse Faraday effect. When circularly polarized light—light that spins as it travels—hits the silver disks, it does not just heat them up. Instead, it pushes the electrons inside the metal to flow in a tight, circular loop. This flowing electricity generates a powerful, localized magnetic pulse right at the surface of the metal. This pulse is strong enough to twist the magnetic moments in the adjacent film, forcing them to form a skyrmion or, if the light is tuned differently, to undo the twist and return the film to a flat, uniform state.

The researchers designed a surface covered in a hexagonal grid of tiny silver disks, each about 120 nanometers wide. They chose this specific arrangement because it creates a resonance, a condition where the light waves bounce around in perfect sync, greatly amplifying the effect. When they shone a laser pulse with a specific spinning direction onto this surface, the silver disks generated a magnetic field pulse reaching about 0.6 tesla. This pulse was delivered directly to a magnetic film made of cobalt, aluminum, and platinum layers sitting right on top of the disks. In computer simulations that modeled the behavior of these materials, a single laser pulse lasting just 20 picoseconds was enough to deterministically create a stable skyrmion. The process was not random; the direction of the light's spin dictated exactly how the magnetic knot formed.

What makes this discovery particularly significant is the ability to reverse the process. The researchers found that by simply flipping the spin direction of the light, they could control the fate of the magnetic knot. If the magnetic film was held in place by a weak external magnetic field, the reversed light pulse would completely unwind the skyrmion, erasing it and leaving the film perfectly smooth and ready for new data. This offers a non-destructive way to delete information, a feature that was missing from previous thermal methods. Even more surprisingly, if the researchers removed that holding magnetic field, the same reversed light pulse did not erase the skyrmion. Instead, it transformed the single knot into a more complex structure called a skyrmionium, which consists of two concentric rings of magnetism. This ability to switch between different topological states—creating a knot, erasing it, or turning it into a double-ring structure—suggests a new way to store multiple bits of information in a single spot.

The simulations showed that this entire cycle happens on a timescale of picoseconds, which is a thousand times faster than the speed of modern computer processors. The process relies on the light creating a transient magnetic field that guides the material through a specific path: first forming a temporary ring of magnetism, which then relaxes into a stable knot. The researchers noted that while their work was conducted through detailed computer modeling using realistic material properties, the physics involved is well-understood. They also addressed concerns about the energy required, pointing out that the actual laser power needed in a real-world experiment is likely much lower than the simulation suggests, keeping the delicate silver structures safe from damage. By proving that light can directly and reversibly control these magnetic textures without heat, this work opens a path toward high-speed, reconfigurable devices that could revolutionize how we store and process information.

Technical Summary: Plasmonic Metasurfaces for Magnetic Skyrmion Control via the Inverse Faraday Effect

Problem Statement
Magnetic skyrmions are promising candidates for next-generation spintronic memory, logic devices, and neuromorphic computing due to their nanoscale dimensions, topological protection, and low-current mobility. However, current methods for the targeted, on-demand writing and erasing of skyrmions face significant limitations. Conventional optical and electrical manipulation schemes rely predominantly on local thermal excitation or ultrafast thermal demagnetization. These thermal mechanisms are inherently stochastic, failing to reliably control the exact number, position, or chiral state of nucleated quasiparticles. Furthermore, purely thermal approaches lack a non-destructive mechanism to selectively "erase" individual skyrmions or lattices without macroscopically perturbing the surrounding magnetic state. Additionally, existing protocols struggle to selectively control the topological charge, making the on-demand discrimination between distinct quasiparticles (e.g., skyrmions vs. skyrmioniums) difficult to achieve.

Methodology
The authors propose a deterministic, field-driven paradigm utilizing a magneto-plasmonic metasurface to achieve ultrafast, all-optical control of magnetic skyrmions. The methodology integrates three core components:

Metasurface Design: A hexagonal lattice of silver (Ag) nanodisks (radius $r$ , thickness $t=10$ nm) is engineered to support Surface Lattice Resonances (SLRs). These resonances arise from the coherent coupling between localized surface plasmons and in-plane diffractive orders.
Inverse Faraday Effect (IFE) Mechanism: Upon illumination with circularly polarized light, the metasurface generates "super-circular" optical spin densities (where local angular momentum density exceeds that of a vacuum plane wave). This drives intense, non-dissipative, circulating drift photocurrents within the nanodisks.
Micromagnetic Simulation: Using MuMax3, the authors simulate the interaction between the generated picosecond magnetic field pulses and an adjacent chiral magnetic multilayer stack ([Co(1.3)/Al(3)/Pt(3)] nm). The simulations incorporate experimentally measured parameters, including interfacial Dzyaloshinskii–Moriya interaction (DMI), saturation magnetization, and exchange stiffness. The optical excitation is modeled using distinct pulse durations: a 20 ps FWHM pulse for nucleation (writing) and a 100 ps FWHM pulse for erasure, with peak intensities up to 12–15 GW/cm².

Key Contributions and Results

Enhanced Optomagnetic Fields: By optimizing the lattice period ( $p=595$ nm) and excitation wavelength ( $\lambda \approx 750$ nm), the metasurface achieves a local electric field enhancement factor of $\approx 90$ . This drives a super-circular optical spin density ( $|s_z| \approx 4000$ ), resulting in localized, out-of-plane magnetic field pulses of approximately 0.6 T (600 mT) at the nanodisk centers. This field strength is sufficient to drive deterministic nucleation without external magnetic fields.
Deterministic Skyrmion Nucleation: The simulations demonstrate that a single optical pulse can deterministically nucleate stable Néel skyrmion crystals. The process follows a transient Bloch-to-Néel relaxation pathway:
- The optical helicity dictates the initial circulation of the spin texture (Bloch-like).
- Interfacial DMI subsequently relaxes this texture into a stable Néel configuration.
- The chirality of the resulting skyrmion (Clockwise vs. Counter-Clockwise) and its core polarity are strictly controlled by the incident light's helicity and the initial magnetization state of the film.
Thermal Assistance: The study reveals that thermal fluctuations (at 300 K and 450 K) assist the switching process by lowering the required optical energy barrier for nucleation without introducing stochastic fragmentation, thereby expanding the operational parameter window.
Reconfigurable Topological Control: The platform enables reversible manipulation of topological states based on the presence of an external bias field ( $B_{bias}$ $B_{bia s}$ ):
- Erasure: Under a confining perpendicular bias field ( $B_{bias} = -50$ mT), a second pulse with reversed helicity (specifically a 100 ps FWHM pulse) deterministically unwinds pre-existing skyrmions, restoring the uniform ground state ( $Q=0$ ).
- Skyrmionium Formation: In the absence of a bias field ( $B_{bias} = 0$ mT), the same reversed-helicity pulse acts on the expanded core of a pre-existing skyrmion, reversing the inner magnetization while preserving the outer domain wall. This deterministically transforms the skyrmion into a stable skyrmionium (a higher-order topological texture with $Q=0$ ).
Selection Rules: The authors establish comprehensive selection rules for writing, erasing, and generating higher-order textures based on pulse fluence, thermal effects, field landscapes, and the matching of stack chirality (DMI sign) with the IFE field polarity.

Significance
The paper claims to establish a scalable foundation for high-speed, reconfigurable topological data storage and unconventional computing architectures. By bypassing the stochasticity and structural damage associated with thermal nucleation, this magneto-plasmonic platform offers a non-destructive, deterministic mechanism for targeted skyrmion manipulation on picosecond timescales. The ability to reversibly switch between distinct topological states (uniform, skyrmion, and skyrmionium) using only the helicity of light and weak bias fields addresses a fundamental bottleneck in the field. This work bridges nanophotonics and magnetism, demonstrating that fully reversible topological control is achievable through the inverse Faraday effect in engineered metasurfaces, providing a pathway toward ultrafast, all-optical spintronic devices.

Technical Summary: Plasmonic Metasurfaces for Magnetic Skyrmion Control via the Inverse Faraday Effect

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