Science & Technology (Commonwealth Union) – Magnetic fields have been the focus of a variety of scientific applications across many decades.
Ferromagnets are the familiar type of magnet that pulls in metal and holds notes on refrigerator doors. Antiferromagnets, by contrast, conceal their magnetic order at the atomic level, yet are gaining attention for their promising technological uses.
A recently identified third class, known as altermagnets, may potentially combine the advantages of both. Discovered only within the past decade, they are being explored for their potential to enable faster and more energy-efficient electronic devices.
Researchers at the University at Buffalo are now suggesting a quantum sensing approach that could make it easier to detect and identify altermagnets.
In a study published in Physical Review Letters, the team outlines a theoretical method that would examine how a suspected altermagnet affects a tiny magnetic defect in a nearby diamond. Changes in how the defect’s magnetic signal relaxes could serve as evidence of altermagnetic behaviour.
The corresponding author Jamir Marino, PhD, assistant professor in the Department of Physics at the University at Buffalo College of Arts and Sciences indicated that this could mark the first step toward a new generation of experiments designed to identify whether a material is an altermagnet.
He further pointed out that altermagnets have the potential to transform how information is transmitted, but to verify this elegant theory, they need experimental methods that can reliably detect them and confirm they behave as predicted by scientists.
The study also includes Marino’s former collaborators Libor Šmejkal and Jairo Sinova, physicists at Johannes Gutenberg University of Mainz, who originally introduced the concept of altermagnetism.
Sinova indicated that this sensing approach could become a key tool for investigating potential altermagnetic materials. He further pointed out that it provides advantages over traditional experimental methods by revealing subtle directional magnetic structures across different regions of a material while causing minimal disturbance.
In 2019, researchers at Mainz encountered a phenomenon that could not be accounted for within the frameworks of either ferromagnetism or antiferromagnetism. Their theoretical calculations indicated that ruthenium dioxide should exhibit zero overall magnetization, similar to an antiferromagnet, yet still respond to an electric current in a way characteristic of a ferromagnet.
This unexpected behaviour led to the emergence of a new idea: altermagnetism.
In conventional magnetic materials, atomic arrangements and electron spins tend to follow straightforward patterns. In ferromagnets, the spins of neighbouring electrons align in the same direction, generating a measurable external magnetic field. These aligned states can be reversed fairly easily, which makes them useful for digital memory applications.
By contrast, antiferromagnets feature alternating, oppositely aligned spins that cancel each other out, resulting in no net magnetism. Although this configuration is more difficult to control, it can switch at much higher speeds, offering promising possibilities for faster and more energy-efficient data storage and processing technologies.
Altermagnets are more intricate in their behavior. While their overall magnetism cancels out, as in antiferromagnets, their crystal structure makes electrons act in ways that resemble ferromagnets.
Marino indicated that this configuration enables altermagnets to merge the fast switching capabilities of antiferromagnets with some of the more easily tunable electronic characteristics of ferromagnets.
Researchers at Mainz and other institutions have already detected experimental signs of altermagnetism in a range of materials. However, theoretical models indicate that over 200 compounds could exhibit altermagnetic properties—more than twice the number of known ferromagnetic materials.
To investigate this possibility, Marino’s group created a quantum sensing approach. The method places a candidate altermagnet near a diamond engineered with a tiny magnetic defect formed by a nitrogen atom next to a missing carbon atom. These defects are extremely sensitive to subtle changes in nearby magnetic fields.
“You don’t want your measurement to strongly perturb the material you’re studying because it can become harder to tell whether you’re seeing the material’s natural behavior or behavior caused by the experiment,” explained Marino.
