For the first time in almost a century, physicists have discovered an entirely new type of magnetic material.
Dive into any physics textbook, and you’ll find magnetic materials divided into two main categories: ferromagnets and antiferromagnets. Ferromagnets are the more familiar type, known for their ability to hold notes on a fridge or guide a compass needle north, thanks to their magnetic fields. Antiferromagnets, while lacking external magnetic fields, possess unique magnetic properties.
This longstanding duo has now expanded into a trio with the identification of a new class of magnetic materials known as altermagnets, which could pave the way for faster, more efficient computer hard drives.
“The principle of altermagnets is quite straightforward,” states Igor Mazin, a theoretical physicist at George Mason University in Fairfax, Virginia. “It’s quite remarkable that this possibility had been overlooked until now.” He expresses surprise at how a third type of magnetic material could have gone unnoticed for so long, given that the study of magnetism dates back thousands of years.
Ferromagnets have been known since ancient times, with lodestone, a naturally magnetized form of magnetite, intriguing the ancient Greeks. The Chinese were using this mineral for compasses as early as the fourth century B.C. Antiferromagnets were not discovered until the 1930s.
More recently, theoretical work predicted the existence of altermagnets. When researchers began searching, they quickly found that these materials were not only real but also abundant.
On a microscopic scale, altermagnets derive their magnetic properties from the spins of their atoms, a quantum mechanical attribute given by electrons. Unlike ferromagnets, where atomic spins align uniformly, or antiferromagnets, where spins alternate direction, altermagnets have spins that not only alternate but are also rotated relative to each other.
This unique arrangement, akin to an M.C. Escher drawing where shapes tessellate and rotate, confers a unique symmetry on altermagnets, placing them in a category of their own, as argued by Jairo Sinova and colleagues from Johannes Gutenberg University Mainz in a September 2022 issue of Physical Review X.
Experimental validation of altermagnet properties is underway, with recent studies confirming their unique electron behaviors. This could lead to denser magnetic storage and faster data operations, overcoming some of the limitations of current magnetic technology.
Altermagnets are found in multiple materials and exceed the number of known ferromagnets. They are non-toxic and well-understood by researchers, indicating a promising future in both existing and novel technological applications.
Their combined properties could make altermagnets particularly useful in technology. Currently, ferromagnets are essential in magnetic hard drives, but they have limitations due to their magnetic fields. Altermagnets, having no net magnetic field but capable of electron spin-splitting, might offer an optimal solution, merging the best of both ferromagnets and antiferromagnets.
With properties that blend the best of both traditional magnetic types along with unique characteristics, altermagnets are breaking through longstanding barriers and could significantly enhance how memory storage and processing devices are made.
