At colder temperatures, the rotations of the material form random patterns, where each pattern rotates like a helix with a particular twist. When heating the material, the turns choose one of the particular helix patterns, a phenomenon that usually occurs when the temperature decreases in magnetic materials. Credit: Radboud University
Physicists observed a very strange new type of behavior in a magnetic material when heated. When the temperature rises, the magnetic spins “freeze” in a static pattern, a phenomenon that usually occurs when the temperature decreases. His findings were published in Nature Physics today, July 4th.
Scientists discovered the phenomenon in neodymium material, an element they described as a “self-induced rotating glass” a few years ago. Rotating glasses are usually alloys where iron atoms, for example, are randomly dispersed in a grid of copper atoms. Each iron atom behaves like a small magnet or a twist. These randomly placed turns point in all different directions.
“It’s pretty counterintuitive, like water that becomes an ice cube when heated.” – Alexandre Khajetoorians
Neodymium is not like conventional rotating glasses, where there is a random mixture of magnetic materials. It is an element and without significant amounts of any other material, it has a glass behavior in its crystalline form. The twists form patterns that rotate like a helix, and this twist is random and constantly changing.
Solid pattern when heated
In this new study, physicists discovered that when they heated the neodymium from -268 ° C to -265 ° C (-450 ° F to -445 ° F), the spins “freeze” in a solid pattern forming a type of d. ‘magnet. , at the highest temperature. Upon cooling the material, the random rotating helix patterns returned. “This‘ freezing ’of the pattern does not normally occur in magnetic material,” says Alexander Khajetoorians, a professor of scanning probe microscopy at Radboud University.
Temperature increases energy in a solid, liquid or gas. The same goes for a magnet: with more temperature, the twists start to shake. “The magnetic behavior of the neodymium we observed is actually the opposite of what happens ‘normally.’ It’s quite counterintuitive, like water that becomes an ice cube when heated,” says Khajetoorians.
Such phenomena are not often found in nature. Very few materials are known to behave incorrectly. Another well-known example is the Rochelle salt, where the charges accumulate and form an ordered pattern at a higher temperature, where at a lower temperature they are randomly distributed.
How it works
The complex theoretical description of spin glasses was the subject of the Nobel Prize in Physics awarded in Paris in 2021. Finding out how these spin glasses work is also important for other scientific fields. If we can finally model how these materials behave, this could also be extrapolated to the behavior of a wide range of other materials.
The underlying strange behavior was related to the concept of degeneration: where many different states have the same energy and the system is frustrated. The effect of temperature is to break this situation: certain states survive, allowing the system to be clearly installed in a pattern. We can also take advantage of this behavior toward new types of information storage or computational concepts, such as brain-like computing.
Reference: “Thermally induced magnetic order from glassiness in elemental neodymium” by Benjamin Verlhac, Lorena Niggli, Anders Bergman, Umut Kamber, Andrey Bagrov, Diana Iusan, Lars Nordström, Mikhail I. Katsnelson, Daniel Wegner, Olle Eriksson and Alexander A. Khajetoorians , July 4, 2022, Nature Physics.DOI: 10.1038 / s41567-022-01633-9