Scientists have long known that magnetism is produced by the spins of electrons that are aligned in a particular way. But about 10 years ago, they discovered another layer of amazing complexity in magnetic materials. Under the right conditions, these spins can act like particles and form small whirlpools or whirlpools that move around independently of the atoms that produced them.
Small swirls are called SkyrmionIs named after Tony Squam, a British physicist who predicted their existence in 1962. Its small size and sturdy properties (like knots that are difficult to undo) have created a rapidly expanding field that better understands them and concentrates on taking advantage of strange properties.
“These objects represent some of the most sophisticated forms of magnetic order we know,” said Stanford Institute for Materials and Energy Sciences, a staff scientist at the SLAC National Accelerator Institute at the Ministry of Energy. Josh Turner, Senior Researcher at SIMES), said. With SLAC.
“Once the skyrmions are formed, they occur all at once throughout the material. What’s more interesting is that the skyrmions move around as if they were separate, independent particles. This means that all spins communicate. It’s like a dancing dance. They move together to control each other. motion Skyrmion, and in the meantime lattice Just sit there under them. “
They are very stable, about 1,000 times larger than atoms, and can be easily moved by passing a small current, so there are many ways to use them for new types of computing and memory storage. I have the idea of a technology that is smaller and uses less energy. “
However, what is most interesting to Turner is the basic physics behind how skyrmions are formed and work. He and his colleagues at DOE’s Lawrence Berkeley National Laboratory and the University of California, San Diego have used SLAC’s Linac Coherent Light, an X-ray free electron laser, to set a precedent for Skyrumion’s natural, undisturbed activity. We are developing a way to capture in no detail. Source (LCLS). This allows you to measure details on a nanoscale (about one millionth of an inch) and observe changes that occur in billions of seconds.
A recent series of treatises describes experiments that suggest that skyrmions can form glass-like phases. In this phase, it looks very slow and stuck, like a car in a traffic jam. In addition, they measure how the natural movements of skyrmions relative to each other oscillate and change in response to applied magnetic fields, and it appears that this inherent movement never stops altogether. I found that.According to Turner, this ever-present variation indicates that skyrmions may have much in common with high temperatures. Superconductor-Quantum materials whose ability to conduct electricity at relatively high temperatures without loss may be related to changes in electron spins and charge streaks.
The researchers observe skyrmion fluctuations in a thin magnetic film made of many alternating layers of iron and gadolinium by taking snapshots using an LCLS X-ray laser beam at intervals of only 1/350 trillion seconds. I was able to do. They state that they can use their methods to study the physics and topologies of different materials. This is a mathematical concept that describes how an object’s shape deforms without radically changing the properties of the object. In the case of skyrmions, the topology gives the skyrmions robust properties and makes them difficult to extinguish.
Sujoy Roy, Staff Scientist at Berkeley Lab’s Advanced Light Source, said: “There is a huge amount of research that can be done on superconductors, composite oxides, magnetic interfaces, etc.”
Sergio Montoya, a scientist at the University of California, San Diego’s Center for Memory and Recording Research, who designed and created the materials used in this study, added: It works for the entire document, not just one small place. “
Quick snapshot of atomic scale changes
Montoya began research on iron gadolinium membranes around 2013. At that time, it was already known that applying a magnetic field to a particular magnet formed a skyrmion lattice, and there was a strong research effort to discover new materials that could contain skyrmions at room temperature. .. Montoya adjusted the growth conditions to adjust the properties of the skyrmion lattice and carefully created the layered material. “Material design and adjustment play a major role in such research,” he said, working with Roy to examine them. X-rays from advanced light sources.
Meanwhile, Turner and his team at LCLS have developed new tools like cameras for taking snapshots of atomic scale fluctuations at very fast shutter speeds. Two X-ray laser pulses, each one millionth of a second long, hit the sample at intervals of one millionth to one billionth of a second. X-rays fly to the detector, each forming a unique “speckle pattern” like a fingerprint, revealing subtle changes in the complex structure of the material.
“We use very low intensity soft X-ray pulses that do not disturb the sample,” explained LCLS scientist Matt Seaberg. “This allows us to take two snapshots that reveal the inherent variation of the material and how it changes in a very short time between them.”
It wasn’t long before the teams at LCLS, Berkeley Labs, and the University of California, San Diego joined forces to point this new tool at Skyrmion.
As Turner said, “Imagine getting a telescope and choosing where to point it first. Skyrmion seemed like a good choice. Many unknowns about its behavior. It is an exotic magnetic structure with. “
More powerful tools in the future
Based on what they saw in these experiments, “We basically believe that the interaction between adjacent skyrmions may be their essential cause. vibration“We are still trying to understand that. It is difficult to know exactly what is vibrating from the type of measurement we made. What is happening and I We had a lot of discussion about how we could understand what the signals we measured really meant. “
The special equipment they built for these experiments was then disassembled to give way to others. However, it will be reassembled as part of a new experimental station that is part of a major upgrade of LCLS. This is an ideal place to continue this new class of experimentation on changes in materials such as superconductors and is a fruitful collaborative science. A trip that Montoya describes as a “fun ride”.
“It’s worth noting how much we’re learning about this kind of magnetic material with the special features of LCLS. This project was a lot of fun. Work with a great team and try a lot. There is literally a treasure trove of information waiting to be discovered. ”
V. Esposito et al, Skyrmion variation at the first-order phase transition boundary, Applied Physics Letter (2020). DOI: 10.1063 / 5.0004879
L. Shen et al, Snapshot Review — Quantum Material Fluctuations:
From skyrmions to superconductivity Advances in MRS (2021). DOI: 10.1557 / s43580-021-00051-y
MH Seaberg et al, Spontaneous variation of magnetic Fe / Gd skyrmion lattice, Physical Review Study (2021). DOI: 10.1103 / PhysRevResearch.3.033249
NG Burdet et al, Absolute Contrast Estimate of Soft X-ray Photon Fluctuation Spectroscopy Using Variational Droplet Model, Science report (2021). DOI: 10.1038 / s41598-021-98774-3
SLAC National Accelerator Laboratory
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Why skyrmions can have so much in common with glass and high-temperature superconductors
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