In 2019, physicists at Johannes Gutenberg University of Mainz stumbled upon something that shouldn't exist: a material that behaved like a magnet in two contradictory ways at once. That discovery of ruthenium dioxide launched an entirely new category of magnetism, and now University at Buffalo researcher Jamir Marino is proposing a way to find hundreds more like it.
For nearly a century, scientists recognized only two types of magnets. Ferromagnets are the ones we know intimately—the friendly forces that stick notes to refrigerators and organize our kitchen drawers. Antiferromagnets are trickier: their atomic spins cancel each other out, leaving no visible magnetism, yet they hold enormous technological promise because they can switch states far faster than ferromagnets. The discovery of altermagnets, this third category emerging within the last decade, suggests something remarkable may be possible: materials that combine the rapid switching speed of antiferromagnets with the more easily controllable properties of ferromagnets.
Understanding what makes altermagnets special requires zooming into the atomic scale. In ferromagnets, neighboring electron spins all point the same direction, creating a strong external magnetic field. In antiferromagnets, spins alternate direction, canceling out overall magnetism but gaining the ability to flip states with extraordinary speed. Altermagnets are more intricate: their magnetism cancels out like antiferromagnets, yet their atomic structure arranges electrons in ways that produce ferromagnet-like behavior. "That arrangement allows altermagnets to combine the rapid switching behavior of antiferromagnets with some of the more easily controllable electronic properties of ferromagnets," Marino explains. Such a fusion could eventually help create faster, more energy-efficient electronics that transform how we store and process information.
The challenge is identifying them. Theoretical predictions suggest more than 200 materials may be altermagnetic—more than double the known ferromagnetic materials—yet scientists have experimentally confirmed signatures of altermagnetism in only a handful so far. Marino's team, including collaborators Libor Šmejkal and Jairo Sinova from the Mainz group who first proposed altermagnets, has developed an elegant solution published in Physical Review Letters: a quantum sensing system using diamond.
The technique places a suspected altermagnet next to a diamond containing a tiny magnetic defect—created by a nitrogen atom replacing a carbon atom. These defects are extraordinarily sensitive to nearby magnetic behavior. Researchers would rotate the defect's magnetic spin in several directions and measure how quickly it relaxes back to its natural state. If the defect relaxes faster in some directions than others, the pattern would reveal the unusually complex spin arrangement predicted for altermagnets.
What makes this approach revolutionary is its gentleness. Many existing methods for probing altermagnetism strongly disturb the material being studied, risking measurement artifacts that obscure what you're actually observing. The quantum sensing system avoids this pitfall. "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. Sinova adds that the technique "offers advantages over conventional experimental techniques by detecting subtle directional magnetic patterns across different regions of a material without significantly disturbing it."
For now, the system exists only in theory, developed through advanced quantum dynamics simulations. But Marino sees it as foundational. "This could be the first building block of a new generation of experiments that determine whether a material is an altermagnet," he says. The road from theoretical proposal to laboratory discovery is long, yet it represents a crucial step toward unlocking materials that could revolutionize information technology itself.