X-Ray Test Confirms Altermagnetism, a Third Kind of Magnetism Beyond Fridge Magnets

For nearly 90 years, physicists sorted magnets into two classes. A team led by the SLAC National Accelerator Laboratory now reports firm experimental evidence for a third.

In ferromagnets, the kind that hold art to a refrigerator door, all electron spins point the same direction and create an observable magnetic field. In antiferromagnets, discovered in 1933, spins alternate up-down-up-down and cancel out, so there is no net magnetic effect. In 2022, researchers proposed a class called altermagnets, which alternate like antiferromagnets but behave in ways once thought to be exclusive to ferromagnets, such as supporting spin currents.

The proposed explanation is a twist in the crystal. In an altermagnet, the lattice around the "up" spins is rotated relative to the lattice around the "down" spins, a break in symmetry that gives the material its unusual behavior. "In the past few years, scientists have observed phenomena that don't fit neatly into the ferromagnetism-antiferromagnetism dichotomy," said lead author Daniel Jost, an associate scientist at SLAC and the Stanford Institute for Materials and Energy Sciences. "We believe our results provide robust experimental confirmation that this third phase, altermagnetism, is real."

The missing piece was evidence of chirality, or handedness, meaning a material cannot be superimposed on its mirror image, like a left hand and a right-handed glove. An altermagnet should have it. A conventional antiferromagnet should not.

The team studied manganese telluride (MnTe), a material treated as antiferromagnetic for decades until it was suspected of being an altermagnet a few years ago. They took it to the European Synchrotron Radiation Facility in France, to a beamline that produces highly controlled polarized X-rays. "Chiral materials scatter left-handed polarized X-ray beams differently than they do right-handed beams," Jost explained. By comparing the scattering of left- and right-circularly polarized X-rays, the team found a clear chiral signal that should not exist in a conventional antiferromagnet. They finished the initial experiment in 2024 and repeated it in early 2025 with the same result. The work was published in Science.

"This chiral signature gave us the solid experimental ground to say altermagnetism stands in a class of its own," Jost said. Rachel Nickel, a postdoctoral scientist at ESRF who helped run the experiment, said the pace of progress is "incredible" given that altermagnetism was proposed only a few years ago.

The payoff is mainly in spintronics, which uses an electron's spin as well as its charge to store and move information. Ferromagnets are easily disturbed by outside magnetic fields. "If you have a permanent magnet in your pocket and walk by a spintronic device built with ferromagnets, you could start flipping the bits, scrambling the information stored there," Jost said. Antiferromagnets avoid that problem but are nearly invisible, which makes it hard to read data from them. "Altermagnets combine the best of both," he said. They have zero net magnetization, so they are stable, yet they can still generate the spin-polarized currents needed to extract information.

Future work will examine how altermagnetic states can be controlled with light and electricity, with possible uses in quantum technologies, memory devices and data centers. Spintronic devices could be faster, more robust and use significantly less power than today's electronics, though practical altermagnet-based hardware has not yet been built.