Researchers have designed a diamond-based quantum sensor that could help detect altermagnets, a newly discovered type of magnetic material with unusual properties.

For almost 100 years, scientists recognized only two fundamental types of magnets. Now, a much newer class called altermagnets is emerging as one of the most exciting discoveries in physics, with the potential to make future electronics faster and far more energy-efficient.

Researchers at the University at Buffalo have now proposed a new quantum sensing technique that could make these elusive materials much easier to identify. Their theoretical approach uses tiny defects inside diamonds to detect the distinctive magnetic behavior that sets altermagnets apart.

The study was published in Physical Review Letters.

A Diamond-Based Quantum Sensor for Altermagnets

The proposed method works by placing a suspected altermagnetic material next to a diamond containing an extremely sensitive magnetic defect. By observing how the defect’s magnetic signal relaxes over time, scientists could detect the unique magnetic signature expected from an altermagnet.

“This could be the first building block of a new generation of experiments that determine whether a material is an altermagnet,” says corresponding author Jamir Marino, PhD, assistant professor in the UB Department of Physics, College of Arts and Sciences. “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.”

Marino collaborated with Libor Šmejkal and Jairo Sinova of Johannes Gutenberg University of Mainz, the physicists who originally proposed the concept of altermagnets.

“This sensing technique could become a very important tool for exploring candidate altermagnetic materials,” Sinova says. “It offers advantages over conventional experimental techniques by detecting subtle directional magnetic patterns across different regions of a material without significantly disturbing it.”

What Makes Altermagnets Different?

Traditional ferromagnets are the familiar magnets found on refrigerators and in countless everyday devices. Their electron spins line up in the same direction, creating a magnetic field that can be easily controlled. Because those spins can be switched between different states, ferromagnets play an important role in computer memory.

Antiferromagnets, by contrast, arrange neighboring electron spins in opposite directions. Their magnetism effectively cancels itself out, making them more difficult to manipulate. However, they can switch states much faster, making them attractive for future electronic technologies.

Altermagnets combine characteristics of both.

Although they have no overall magnetization like antiferromagnets, their crystal structure causes electrons to behave in ways typically associated with ferromagnets. That unusual combination could allow devices to process and transport information more quickly while using less energy.

“That arrangement allows altermagnets to combine the rapid switching behavior of antiferromagnets with some of the more easily controllable electronic properties of ferromagnets,” Marino says.

A Discovery That Began With an Unexpected Observation

The idea of altermagnetism first emerged in 2019 after researchers in Mainz encountered behavior that could not be explained by either of the two known classes of magnets.

Their calculations suggested that a material called ruthenium dioxide should have no overall magnetization, similar to an antiferromagnet. Yet when an electric current was applied, it behaved like a ferromagnet.

That surprising result led scientists to propose an entirely new category of magnetic materials.

Since then, experimental studies have found signs of altermagnetism in several materials. Theoretical predictions suggest that more than 200 materials could belong to this new class, more than twice the number of currently known ferromagnetic materials.

Why Diamonds Are So Useful

To speed the search for these materials, Marino’s team designed a quantum sensing system based on a special defect inside a diamond.

The defect forms when one carbon atom is replaced by a nitrogen atom and a neighboring carbon atom is missing. These tiny imperfections are remarkably sensitive to nearby magnetic activity.

Researchers would rotate the defect’s magnetic spin in multiple directions and measure how quickly it relaxes. If the relaxation rate changes depending on the direction, it could reveal the complex magnetic patterns predicted for altermagnets.

An important advantage of the technique is that it would disturb the material far less than many existing experimental methods.

“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 says.

A Promising Idea That Still Needs Testing

The sensing system currently exists only as a theoretical proposal based on sophisticated quantum simulations. Laboratory experiments will be needed to determine whether it can reliably identify altermagnets in real materials.

Even so, the researchers believe such a tool could play a major role in bringing altermagnets from theory into practical technology.

“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.”