Абстрактний концепт-арт із двома веселковими стрілками Абстрактний концептуальний малюнок, що показує, як працює альтермагнетизм / Алекс Спід
Researchers have found evidence for the existence of a third class of magnetism — altermagnetism. The discovery will make it possible to create high-speed magnetic drives and facilitate the development of superconductors.
«Previously, we had two well-known types of magnetism. Ferromagnetism, where magnetic moments, which can be thought of as small compass hands on an atomic scale, all point in the same direction. And antiferromagnetism, where neighboring magnetic moments point in opposite directions — you can think of it more like a chessboard of alternating white and black squares»,” says study author Oliver Amin, a doctoral student at the University of Nottingham in the United Kingdom.
The spins of electrons in an electric current point in one of two directions and can align along or opposite these magnetic moments to store or transfer information, forming the basis of magnetic memory devices.
Altemagnetic materials, first created in 2022, have a structure that falls somewhere in between. Each individual magnetic moment points in the opposite direction than its neighbor, as in an antiferromagnetic material. But each one is slightly twisted relative to the neighboring magnetic atom, which leads to some new ferromagnetic properties. The alloys combine the best properties of both ferromagnetic and antiferromagnetic materials.
«The advantage of ferromagnets is that we have an easy way to read and write data in memory using these top or bottom domains. But because these materials have pure magnetism, this information is also easily lost through the touch of a magnet»,” says study co-author Alfred Dal Dean, a doctoral student at the University of Nottingham.
On the contrary, antiferromagnetic materials are much more difficult to manipulate for information storage. Since they have zero magnetism, storing information in these materials is much safer and the transfer speed is better.
While altermagnets have the speed and stability of antiferromagnets, they also have an important property of ferromagnets called the reversal of time symmetry. That is, if it were possible to rewind events in time, the particles would behave the same way. However, since electrons have both quantum spin and magnetic moment, an imaginary reversal of time and direction of motion changes the rotation, i.e., the symmetry is broken.
«If you look at these two electronic systems — one where time is running normally and the other where you rewind, — they look different, so the symmetry is broken. This allows certain electrical phenomena to exist»,” Oliver Amin explained.
The team, led by Peter Wadley, a professor of physics at the University of Nottingham, used a technique called photoemission electron microscopy to image the structure and magnetic properties of manganese telluride, a material previously thought to be antiferromagnetic.
Circularly polarized light revealed the different magnetic domains created by the symmetry breaking in time, while horizontally or vertically polarized X-rays allowed the direction of magnetic moments throughout the material to be measured. By combining the results of both experiments, the researchers created the first-ever map of distinctive magnetic domains and structures in an altermagnetic material.
With this proof-of-concept, the team fabricated a series of altermagnetic devices by manipulating the internal magnetic structures using a controlled thermal cycling technique.
«We were able to form these exotic vortex textures in both hexagonal and triangular devices. These vortices are gaining more and more attention in spintronics as potential information carriers, so this was a good first example of how to create a working device»,” says Oliver Amin.
The authors of the study argue that the ability to image and control this new form of magnetism could revolutionize the design of next-generation memory devices with increased operating speeds and enhanced durability and ease of use. Alternating magnetism will also help in the development of superconductivity: «For a long time, there has been a hole in the symmetry between these two fields, and this class of magnetic materials, which has remained elusive until now, has turned out to be the missing link in the puzzle,» Alfred Dal Dean notes. The study is published in the journal Nature.
Source: Space.com