Researchers have obtained the first conclusive evidence of an elusive third class of magnetismcalled altermagnetism. Their conclusions, published on December 11 in the journal Naturecould revolutionize the design of new high-speed magnetic memory devices and provide the missing piece of the puzzle in the development of better superconductor materials.
“We previously had two well-established types of magnetism,” study author Oliver Aminpostdoctoral researcher at the University of Nottingham in the United Kingdom, told Live Science. “Ferromagnetism, where magnetic moments, which you can imagine as little compass arrows on the atomic scale, all point in the same direction. And antiferromagnetism, where neighboring magnetic moments point in opposite directions, you can imagine it more like a chessboard of alternating white and black tiles.”
Electronic spins within an electric current must point in one of two directions and can align with or against these magnetic moments to store or transport information, thus forming the basis of magnetic memory devices.
A new form of magnetism
Alternagnetic materials, theorized for the first time in 2022have a structure that lies somewhere in between. Each individual magnetic moment points in the opposite direction to its neighbor, as in an antiferromagnetic material. But each unit is slightly twisted relative to that adjacent magnetic atom, giving it ferromagnetic-like properties.
Altermagnets therefore combine the best properties of ferromagnetic and antiferromagnetic materials. “The advantage of ferromagnets is that we have a simple way to read and write to memory using these ascending or descending domains,” study co-author Alfred Dal-Dindoctoral student also at the University of Nottingham, told Live Science. “But because these materials have net magnetism, this information is also easy to lose by passing a magnet over it.”
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Conversely, antiferromagnetic materials are much more difficult to manipulate for information storage. However, because they have zero net magnetism, the information in these materials is much more secure and faster to transport. “Alter magnets have the speed and resilience of an antiferromagnet, but they also have this important property of ferromagnets called time reversal symmetry breaking,” Dal Din said.
This mind-blowing property examines the symmetry of objects moving forward and backward in time. “For example, gas particles fly around, randomly collide and fill space,” Amin said. “If you go back in time, this behavior doesn’t seem any different.”
This means that symmetry is preserved. However, because electrons have both quantum spin and magnetic moment, reversing time – and therefore direction of travel – reverses the spin, meaning the symmetry is broken. “If you look at these two electronic systems – one where time is progressing normally and one where you’re rewinding – they look different, so the symmetry is broken,” Amin explained. “This allows certain electrical phenomena to exist.”
Finding “the missing link” in superconductivity
The team – led by Peter Wadleyprofessor 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 once thought to be antiferromagnetic.
“Different aspects of magnetism illuminate depending on the polarization of the X-rays we choose,” Amin said. Circularly polarized light revealed the different magnetic domains created by time-reversal symmetry breaking, while horizontally or vertically polarized X-rays allowed the team to measure the direction of magnetic moments throughout the material. By combining the results of the two experiments, the researchers created the first-ever map of the different magnetic domains and structures within an altermagnetic material.
With this proof of concept in place, the team fabricated a series of altermagnetic devices by manipulating the internal magnetic structures through a controlled thermal cycling technique.
“We were able to form these exotic vortex textures into hexagonal and triangular devices,” Amin said. “These vortices are attracting more and more attention in spintronics as potential carriers of information, so this was an interesting first example of how to create a practical device.”
The study authors said the ability to image and control this new form of magnetism could revolutionize the design of next-generation memory devices, with increased operating speeds, improved resilience and ease of use. .
“Altermagnetism will also contribute to the development of superconductivity,” Dal Din said. “For a long time there has been a gap in the symmetries between these two areas, and this class of magnetic materials that has remained elusive until now turns out to be this missing link in the puzzle.”