Physicists at the University of Buffalo are now suggesting a quantum sensing method to greatly simplify the identification of altermagnets. The theoretical method would detect how a putative altermagnet disrupts a small magnetic flaw in a neighboring diamond. The study was published in Physical Review Letters.
An illustration of the atomic structure of altermagnets. Neighboring atoms are rotated and their magnetic spins are flipped. Image Credit: Libor Šmejkal & Anna Birk Hellenes.
Traditional magnets, the kind that attract metal and hold photos on refrigerators, are known as ferromagnets. Antiferromagnets, by contrast, hide their magnetism at the atomic scale, yet their unique properties have made them increasingly important for advanced technologies.
Over the past decade, researchers have identified a third class of magnetic materials known as altermagnets. These materials combine some of the most useful characteristics of both ferromagnets and antiferromagnets, offering the potential for faster, more energy-efficient electronic devices in the future.
One way to understand altermagnetism is by examining how the magnetic signal associated with a defect relaxes over time. The distinct relaxation behavior of this signal can reveal the presence of altermagnetic order and help distinguish altermagnets from other types of magnetic materials.
This could be the first building block of a new generation of experiments that determine whether a material is an altermagnet. Altermagnets could completely revolutionize the way we transport information, but to confirm if this elegant theory is true, we need experiments that identify altermagnets and confirm they behave the way scientists predict.
Jamir Marino, PhD, Corresponding Author and Assistant Professor, Department of Physics, College of Arts and Sciences, University at Buffalo
Marino's former coworkers Libor Šmejkal and Jairo Sinova, physicists at Johannes Gutenberg University of Mainz who initially proposed altermagnets, are co-authors of the study.
This sensing technique could become a very important tool for exploring candidate altermagnetic materials. It offers advantages over conventional experimental techniques by detecting subtle directional magnetic patterns across different regions of a material without significantly disturbing it.
Jairo Sinova, Physicist, Johannes Gutenberg University of Mainz
Not a Grandfather’s Magnet
In 2019, the Mainz research team observed an effect that could not be explained by either ferromagnets or antiferromagnets. Their calculations suggested that a material called ruthenium dioxide should exhibit no net magnetization, similar to an antiferromagnet, yet respond to an electric current in a way typically associated with ferromagnets.
This unexpected behavior led to the concept of altermagnetism.
In antiferromagnets, neighboring electron spins are aligned in opposite directions, causing their magnetic moments to cancel each other out and resulting in no overall magnetization. While this alternating spin arrangement makes antiferromagnets more challenging to manipulate, it also enables them to switch states much faster than ferromagnets. As a result, they hold significant promise for faster, more energy-efficient information storage and processing technologies.
Altermagnets are more intricate. Their atomic structure leads electrons to behave in ways often associated with ferromagnets, even though their magnetism cancels out overall, like in antiferromagnets.
That arrangement allows altermagnets to combine the rapid switching behavior of antiferromagnets with some of the more easily controllable electronic properties of ferromagnets.
Jamir Marino, PhD, Corresponding Author and Assistant Professor, Department of Physics, College of Arts and Sciences, University at Buffalo
Diamonds are a Physicist’s Best Friend
Altermagnetism signs have been experimentally detected in a number of materials by the Mainz team and other researchers. However, more than 200 materials (more than twice as many as known ferromagnetic materials) may be altermagnetic, according to theoretical predictions.
Marino's group created their quantum sensing technology for this reason. A diamond with a minor magnetic defect caused by a nitrogen atom and a missing nearby carbon atom is placed next to a putative altermagnet. These flaws are incredibly sensitive to magnetic activity in the vicinity.
Researchers would twist the defect's magnetic spin in different directions and evaluate how soon it relaxed. The abnormally complicated spin pattern expected for altermagnets may be demonstrated if the defect relaxes more quickly in some directions than others.
Most importantly, compared to many current techniques for probing altermagnetism, the quantum sensing device would be less intrusive.
“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,” Marino notes.
Marino emphasizes that the sensing system, which was created using sophisticated models that mimic quantum dynamics, is now just in theory. To determine whether it can accurately detect altermagnetism, more experiments will be required.
“Efficiently identifying altermagnetic materials is a crucial step toward one day actually using them in electronics,” Marino says. “Altermagnets would make transport of information radically more efficient. That could allow technology to scale down and be less power consuming.”
Other co-authors include V.A.S.V. Bittencourt of the University of Strasbourg/Max Planck Institute for the Science of Light and Hossein Hosseinabadi, PhD, a former graduate student in Marino's lab who is currently an independent distinguished postdoctoral scholar at the Max Planck Institute for the Physics of Complex Systems in Germany.
The German Research Foundation provided funding for the study.
Journal Reference:
Bittencourt, V. A. S. V., et al. (2026) Quantum Impurity Sensing of Altermagnetic Order. Physical Review Letters. DOI: 10.1103/2ppn-kvjv. https://journals.aps.org/prl/abstract/10.1103/2ppn-kvjv.