A Quantum Sensor Wants to Find Magnets That Shouldn’t Exist

Let’s say you discovered a creature that looks like a cat and moves like a dog, but somehow has the metabolism of neither. Every zoologist on Earth would lose their minds trying to classify it. Now suppose that creature has been hiding in plain sight inside hundreds of common materials, and nobody had the right pair of glasses to spot it.

That’s basically what’s happening right now in condensed matter physics, except the mystery creature is a magnet, the glasses are a diamond with a deliberate flaw in it, and the zoologists are a team at the University at Buffalo who just published a theoretical blueprint for catching the thing in the act.

The study, published in Physical Review Letters, proposes a quantum sensing technique designed to identify altermagnets, a class of magnetic materials so new that the word itself barely existed before 2020. If the technique works in practice, it could crack open a catalog of over 200 materials that theorists suspect are altermagnetic but nobody can efficiently confirm.

The Magnet Family Had Two Kids for a Century, Then a Third One Showed Up

Since the early 20th century, physicists sorted all magnetic materials into two buckets.

Ferromagnets are the ones you know. Your fridge magnets. The ones whose atomic spins all line up in the same direction, producing the external magnetic field that holds up your grocery list. They’re useful, they’re well-understood, and they have a well-documented weakness. Flipping those aligned spins takes energy and happens at speeds that have practical ceilings.

Antiferromagnets are sort of like the introverts of the magnet world. Their neighboring atomic spins point in opposite directions, canceling out the net magnetism entirely. From the outside, they look like they aren’t magnetic at all. But they switch states much faster than ferromagnets, which makes physicists very interested in them for next-generation data storage and processing. The tradeoff is that their hidden magnetism makes them harder to manipulate and read.

For decades, that was the full family tree. Two branches. Done.

Then in 2019, a team at Johannes Gutenberg University of Mainz, led by physicists Libor Šmejkal and Jairo Sinova, ran calculations on a compound called ruthenium dioxide and got results that didn’t fit either category. The material should have had zero net magnetization, just like an antiferromagnet. But when they modeled an electric current through it, the electrons behaved like they were inside a ferromagnet.

And there’s a reason why.

Because the atomic structure was doing something nobody had a name for yet.

What Makes an Altermagnet an Altermagnet (And Why It’s So Weird)

The key to altermagnetism lives in geometry. In an antiferromagnet, neighboring atoms have opposite spins, and those atoms sit in a simple, mirror-image arrangement. The spins cancel. The structure is symmetric. Everything is tidy.

In an altermagnet, the neighboring atoms also have opposite spins, but they’re rotated relative to each other. That rotation breaks the symmetry in a specific way that gives rise to electronic properties you’d normally only see in ferromagnets, even though there’s no net magnetic field. It’s like two people pulling a rope in opposite directions with equal force (so nothing moves) but each person is standing at a different angle, and that angle changes the physics of everything around them.

This combination is what makes altermagnets so exciting to physicists and materials scientists. They can potentially switch as fast as antiferromagnets and offer electronic control properties closer to ferromagnets. That opens the door to electronics that process information faster and consume less power.

Jamir Marino, the corresponding author on the new UB study, put it plainly in the press release.

“Efficiently identifying altermagnetic materials is a crucial step toward one day actually using them in electronics. (…) Altermagnets would make transport of information radically more efficient. That could allow technology to scale down and be less power consuming.”

Here’s the problem, though. Theoretical predictions suggest more than 200 materials might be altermagnetic. That’s more than double the number of known ferromagnetic materials. And we don’t have a clean, efficient, low-disruption way to confirm which ones actually are.

The Diamond With a Hole in It

This is where the quantum sensing proposal comes in, and honestly, the underlying technology is one of those things that sounds like science fiction until you learn that people have been using it for years.

The sensor in question relies on something called a nitrogen-vacancy center, or NV center, in diamond. Take a diamond crystal lattice. Remove one carbon atom. Replace its neighbor with a nitrogen atom. You now have a tiny, stable, optically addressable quantum defect that is absurdly sensitive to magnetic fields in its immediate environment. Physicists have been using NV centers to detect everything from single electron spins to nanoscale temperature variations. They’re the Swiss Army knife of quantum sensing.

Marino’s team proposes placing a suspected altermagnetic material next to a diamond containing an NV center. Then you’d rotate the defect’s magnetic spin along several different directions and measure how quickly it relaxes, meaning how fast the spin loses its orientation and returns to equilibrium.

The Directional Relaxation Trick

Here’s the clever part. If the material next to the diamond is a boring old ferromagnet or antiferromagnet, the NV center’s relaxation rate should look roughly the same regardless of which direction you orient the spin. The magnetic environment around those materials, though different from each other, doesn’t have the kind of directional asymmetry that would show up in relaxation measurements taken along multiple axes.

But altermagnets, with their rotated atomic arrangements, produce a spin texture that varies depending on the direction you’re looking at it. The NV center’s relaxation rate should change based on its orientation relative to the altermagnet. Faster relaxation in some directions, slower in others. That anisotropy, that directional fingerprint, would be the smoking gun.

It’s much like holding a microphone next to a speaker. If the speaker is playing a single tone, the mic picks up the same thing no matter where you hold it. But if the speaker is producing a complex spatial sound pattern (the audio equivalent of the altermagnet’s spin texture), the mic hears different things depending on its angle. The NV center is the mic. The altermagnet is the weird speaker.

Why Not Just Poke the Material Directly?

A fair question. Several experimental techniques have already detected signatures of altermagnetism in a handful of materials. But many of these methods involve sending currents through the material, applying external fields, or probing with high-energy particles, all of which can disturb the very thing you’re trying to measure. You end up in a Heisenberg-adjacent situation (not the quantum uncertainty kind, but the practical “did I just change the answer by asking the question” kind) where it becomes harder to distinguish the material’s natural behavior from artifacts of the experiment.

The NV center approach, by contrast, sits outside the material. It listens. It doesn’t shout. As Marino said:

“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.”

Jairo Sinova, one of the original architects of altermagnetism theory and a co-author on the new study, agreed that the technique could be “a very important tool for exploring candidate altermagnetic materials” because it “detects subtle directional magnetic patterns across different regions of a material without significantly disturbing it.”

A Theoretical Blueprint, Not a Working Device (Yet)

Credit where it’s due. The team is upfront about the biggest limitation of this work. The sensing system exists only in theory. It was developed using advanced models that simulate quantum dynamics, and real experiments still need to confirm whether the approach can reliably detect altermagnetism in practice.

This matters because the gap between “this should work according to our simulations” and “this works on a bench in a lab” is often measured in years, funding cycles, and at least one deeply frustrating debugging session where the signal disappears every time someone opens the lab door (quantum systems are famously cranky about environmental disturbances.)

The study’s other co-authors, Hossein Hosseinabadi (now at the Max Planck Institute for the Physics of Complex Systems) and V.A.S.V. Bittencourt (University of Strasbourg/Max Planck Institute for the Science of Light), contributed to the theoretical modeling supported by the German Research Foundation.

Altermagnets sit in a sweet spot that neither ferromagnets nor antiferromagnets occupy alone. If even a fraction of those 200+ predicted materials turn out to be genuinely altermagnetic, and if their properties hold up under experimental scrutiny, the implications for energy-efficient electronics, spintronics, and information processing are significant.

But “if” is doing a lot of heavy lifting in that sentence.

The Promise Lives in the Plumbing

What makes the UB proposal interesting is that it offers a potentially scalable, minimally invasive method for screening candidates. Right now, confirming altermagnetism in a single material is a research project unto itself. If the NV-center approach works, it could become more like a diagnostic test, something you run on a material the way you’d run a blood panel, to see if it exhibits the directional relaxation signature that says “yeah, this one’s probably altermagnetic, go ahead and do the full workup.”

That’s the dream, anyway. And it’s a good dream.

The reality is that we’re still in the phase where the diagnostic test itself hasn’t been tested. The theory is elegant. The physics checks out on paper. The team has genuine credibility, including co-authors who literally invented the concept of altermagnetism. All the ingredients for a successful experimental validation are in place.

But quantum experiments have a long and storied history of not cooperating with elegant theories on the first (or fifth) attempt. So for now, the proposal is a well-constructed argument that diamonds might be able to identify a new kind of magnet that we think exists but can’t yet efficiently confirm. Which, honestly, is a perfectly normal Tuesday in quantum physics. The field runs on “we’re pretty sure this should work” until one day, in some lab, it does.