Small in-plane magnetic fields switch skyrmion chirality and improve lattice order in a two-dimensional magnet, pointing to low-energy control of spin textures for future computing devices.
(Nanowerk Spotlight) Magnetic data storage has moved through several revolutions, shifting from spinning disks to solid-state devices and now toward components that promise speed, resilience, and very low energy use. A central theme in this evolution is how to encode information in ever smaller structures without sacrificing stability or control. One emerging approach centers on skyrmions, which are nanoscale whirlpools of spin inside magnetic materials.
A skyrmion forms when the direction of the magnetic moments in a material twists in a circular pattern, creating a vortex-like structure that behaves like a particle. These spin patterns resist simple erasure because of their topology, which describes how the pattern loops around itself. That makes skyrmions strong candidates for magnetic computing and storage.
Control has been the sticking point. Skyrmions are difficult to manipulate without destroying their structure or using large currents that generate heat. A property called chirality, which refers to whether the twist pattern is left-handed or right-handed, is especially hard to switch once it is set.
Chirality matters because it affects how skyrmions interact and move. Previous research often used engineered interfaces between magnetic and heavy metal layers to stabilize skyrmions, but these setups created only one type of chirality and left little room for change.
Meanwhile, two-dimensional magnetic crystals called van der Waals magnets have opened new possibilities. These materials are held together by weak forces between layers, so they can be made thin and are easy to manipulate. They also respond well to magnetic fields, making them useful for exploring skyrmion behavior. Tools like Lorentz transmission electron microscopy, which can image magnetic structures in real time at low temperatures, now allow researchers to observe skyrmion dynamics directly.
Manipulating the energy landscape of CrBr3 with in-plane magnetic fields. a) Schematic depiction of experimental LTEM setup, where tilting the sample relative to the electron beam produces an in-plane component of the magnetic field (Bip). b) Schematic of the energy landscape of the system, with Bloch skyrmionic bubbles as the ground state and an energy barrier (ΔE) between type-II bubbles and opposing chiralities. c) Experimental LTEM image of a mixed Bloch skyrmionic bubble lattice at 13 K, stabilized by field cooling at Boop = 30 mT. d) Reconstruction of the magnetic induction of blue box in part (c) showing the mixed chiralities of skyrmionic bubbles. e) Tilting the sample in LTEM creates an in-plane field component which creates a lattice of type-II bubbles. f) Reconstruction of the magnetic induction of pink box in part (f) showing alignment of domain walls in the type-II bubbles. g–h) Micromagnetic simulations of a Bloch skyrmionic bubble lattice at Bip = 0 mT (g) and at Bip = 17 mT (h), with Boop = 500 G. The scale bar is 200 nm. i-j) Simulated LTEM images of the simulations in parts g and h, respectively. k) Micromagnetic energies as a function of Bip, starting and ending at the states shown in parts (g) and (h), respectively. (Image: Reprinted from DOI:10.1002/adma.202513067, CC BY) (click on image to enlarge)
The material studied is chromium tribromide, also called CrBr3. This van der Waals magnet can be exfoliated into flakes about one hundred nanometers thick, where its magnetic ordering takes on new forms. When cooled below a critical temperature, these flakes host circular magnetic regions called Bloch-type skyrmion bubbles. In a Bloch-type bubble, the spins along the edge rotate around the bubble wall. Whether they rotate clockwise or counterclockwise determines the chirality.
The researchers first cooled the sample to 13 Kelvin and applied an out-of-plane magnetic field, meaning a field perpendicular to the surface of the crystal. This created a stable but disordered array of skyrmion bubbles with mixed chirality. The bubbles did not arrange into any ordered lattice. Their positions, orientations, and chirality were random, creating a patchwork that resembled a magnetic liquid rather than a crystal.
The turning point came when a second magnetic field was applied in the plane of the sample. This in-plane field was much weaker than the first, but it had a very specific effect. It reduced the energy barrier between skyrmions of opposite chirality by introducing a temporary intermediate structure called a type-II bubble.
A type-II bubble is not a skyrmion. Its spin pattern is simpler and lacks a protected twist. That makes it an accessible transition state between left-handed and right-handed skyrmions. When the energy difference between the skyrmion and type-II state became small enough, random thermal motion could push the system over the barrier and make the bubble flip chirality.
The chirality switching was spontaneous and reversible. At just a few millitesla of in-plane field strength, the researchers observed several flips per minute in their microscope images. As the field was increased, the number of flips rose sharply. When the in-plane field became too strong, the bubbles lost their circular skyrmion structure altogether and became type-II bubbles permanently. That marked the upper limit for usable switching.
Computer simulations supported the experimental observations. The simulations showed how the different contributions to the magnetic energy changed with the in-plane field. The most important change was a reduction in magnetostatic energy, which is the energy cost of stray magnetic fields near the bubble.
Lowering this energy made the type-II state more favorable and reduced the barrier to chirality switching. The simulations also confirmed that the switching was driven by thermal activation, not direct forcing by the magnetic field.
A second effect emerged during switching. The number of bubbles of each chirality was not equal. One chirality gradually became more common than the other. This imbalance came from a weak interaction in the material called the Dzyaloshinskii-Moriya interaction. This interaction slightly favors one direction of spin rotation over the other, giving that chirality a small energy advantage. When combined with the torque from the out-of-plane field, it created a preferred handedness during the switching process.
Reversing the direction of the out-of-plane field, or changing the sign of the Dzyaloshinskii-Moriya interaction, would reverse the preference.
The researchers also studied how the switching affected the larger skyrmion lattice. At the start of the experiment, the skyrmion bubbles formed a disordered, liquid-like pattern with many defects. As chirality switches continued, the bubbles began to shift. Defects moved. Grain boundaries rearranged. Over several minutes, the array settled into a more ordered phase called a hexatic.
In a hexatic phase, each bubble has six neighbors arranged at roughly equal angles. The distances between the bubbles are still somewhat fluid, but the angular order becomes strong. This phase represents a kind of halfway point between a liquid and a true crystal.
The ordering occurred because each bubble stretches slightly when it moves into the type-II state. That stretching happens along the direction of the in-plane field. As the bubbles repeatedly stretch and relax during switching, they exert small forces on their neighbors. Those forces shake defects loose and help the array settle into a lower energy configuration.
When only the out-of-plane field was applied, no ordering took place. At high out-of-plane field strength the bubbles disappeared entirely. This confirmed that the in-plane field plays a unique role in both switching and ordering.
The study shows that chirality is not just a static property. It can be tuned and flipped using simple magnetic fields at low temperatures. This makes it useful for storing information in magnetic memory devices. The randomness that drives switching can be controlled by the strength of the field. That could be valuable in probabilistic or neuromorphic computing, which depends on tunable noise.
The ability to organize skyrmion arrays without high current or complex fabrication also has promise for future magnetic logic or memory chips.
By demonstrating both chirality switching and field-assisted lattice ordering in a two-dimensional magnet, the work provides a blueprint for using magnetic fields to manipulate skyrmions at multiple scales. The key point is that even weak in-plane fields can reshape the magnetic energy landscape enough to enable chirality flips and improve lattice order. That combined control moves skyrmion research closer to real devices and shows how field-programmable spin systems could be built from simple, layered materials.
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