In 2022, physicists discovered altermagnets—a third type of magnetism that somehow combines the best qualities of the two previous types of magnetism. These unique magnets are difficult to identify, but a new proposal using quantum sensors might help make things easier.
In a recent paper published in Physical Review Letters, physicists describe a theoretical technique that tracks the presence of an altermagnet by observing how it affects tiny magnetic defects in diamond. Altermagnets are known to have distinctive spin patterns, which can be traced back to how quickly diamond defects relax after being rotated. If current theories are correct, altermagnets could “completely revolutionize the way we transport information,” Jamir Marino, the study’s co-author and a physicist at the State University of New York at Buffalo, said in a statement.
But first, we’ll need to see whether any of the 200+ materials suspected to be altermagnets truly do behave as predicted, the team added in the statement. Marino noted that the approach “could be the first building block of a new generation of experiments that determine whether a material is an altermagnet.”
The spins in a magnet
The team behind the new study includes researchers involved in the original discovery of altermagnets. According to the statement, before this finding, researchers believed there were two main types of magnetism: ferromagnets and antiferromagnets. The former are the “classic” magnets, like stuff you stick on a fridge, whereas the latter refer to materials that display a complex magnetism at the atomic level.
The primary difference between the different types of magnetism has to do with the organizational patterns of atoms and their electron spins. In ferromagnets, neighboring electron spins align in the same direction. On the other hand, neighboring spins point in opposite directions in antiferromagnets. Although the former is easier to control, the latter has shown more promise in energy-efficient information storage and processing, the team explained in the statement.
Altermagnets are a mix of the two in that their electrons cancel each other out like antiferromagnets, but their atomic structure overall makes them behave like ferromagnets. According to Marino, this means that altermagnets “combine the rapid switching behavior of antiferromagnets with some of the more easily controllable electronic properties of ferromagnets.”
Tracing a ripple
The altermagnetic “detector” utilizes quantum noise spectroscopy. The detector design involves introducing a tiny magnetic defect in diamond, created by one nitrogen atom and a missing neighboring carbon atom. These defects are extremely sensitive to magnetic behavior.
If an altermagnet is nearby and researchers try rotating the defect’s magnetic spin, the defect would relax faster in some directions than others, the team explained. Importantly, this approach is less invasive than existing methods to search for altermagnets. It’s also presumably less hefty than existing methods, which can require giant particle accelerators.
“You don’t want your measurement to strongly perturb the material you’re studying,” explained Marino. “It can become harder to tell whether you’re seeing the material’s natural behavior or behavior caused by the experiment.”
So far, the team has only confirmed that the technique could work via advanced quantum dynamics simulations. Accordingly, researchers will have to carry out empirical tests to see if the method can reliably detect altermagnetism. If they’re successful, however, this will provide researchers with an easier way to find magnetic materials with significant technological potential.
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