Altermagnetism Confirmed: Physicists Prove a Third Form of Magnetism in MnTe

For nearly ninety years, physics textbooks have sorted magnets into two kinds, and that sorting has now broken. A team led by the U.S. Department of Energy's SLAC National Accelerator Laboratory reports in Science this week that it has delivered conclusive experimental proof of a third magnetic phase, called altermagnetism, in the material manganese telluride (MnTe). It is the kind of result that does not just add a fact to a field; it adds a chapter to the textbook.

The old picture is simple enough to hold in your head. In a ferromagnet, the spins of the electrons — their internal angular momentum, pointing "up" or "down" — all line up in the same direction, producing the magnetic field that holds a note to a fridge door. Humans have used ferromagnets since ancient times. In 1933, physicists found the second kind: antiferromagnets, in which spins alternate up-down-up-down and cancel each other out, leaving no net magnetic effect. That two-way split held for almost a century, until some materials started misbehaving. They showed the alternating spins of an antiferromagnet, yet could still carry spin-polarized currents the way a ferromagnet can — two behaviors that were supposed to be mutually exclusive. In 2022, researchers gave the misfits a name: altermagnets.

The theory behind the name is a geometric twist. An altermagnet's spins alternate like an antiferromagnet's, but the crystal lattice around the "up" spins is rotated relative to the lattice around the "down" spins. That broken symmetry, the theory said, should give the material a handedness — a chirality, like a left hand that cannot fit a right-handed glove — that an ordinary antiferromagnet lacks. By 2024, several lines of evidence pointed that way, but the decisive piece was still missing: nobody had directly observed the chirality itself.

That is what the SLAC-led team went looking for, and they found it in MnTe, a material long classified as an ordinary antiferromagnet. Working at the European Synchrotron Radiation Facility in France, on a beamline built to produce precisely controlled polarized X-rays, they scattered circularly polarized X-rays off the material and compared how it responded to left-handed versus right-handed light. A non-chiral material would scatter both beams identically; MnTe did not. The chiral signal was clear, and when the team repeated the experiment in early 2025, it held. Lead author Daniel Jost calls it "solid experimental ground to say altermagnetism stands in a class of its own."

Why should anyone outside a physics department care? Because of spintronics, the effort to build electronics that use an electron's spin as well as its charge, promising devices that are faster, tougher, and far less power-hungry — a real consideration for data centers. The two old kinds of magnet each fail in opposite ways. Ferromagnets are too easily disturbed: as Jost puts it, a permanent magnet in your pocket could flip the bits of a ferromagnet-based device as you walk past. Antiferromagnets solve the stability problem but are practically invisible, so reading the data back out, or driving a useful spin current through them, is hard. Altermagnets promise both at once: zero net magnetization, so they are stable, plus the spin-polarized currents needed to read information easily. That combination is why the paper points toward memory devices, quantum technologies, and data centers rather than toward a museum shelf.

There are two honest caveats, and both matter. First, this is proof in one material, confirmed by one team's technique; the field now has to show that the signature generalizes and that altermagnetic states can be controlled with light and electricity, which the researchers name as the next step. Second, no device exists yet. The road from a synchrotron beamline to a memory chip runs through years of materials engineering, and plenty of beautiful physics never makes that trip. The encouraging sign is the pace: the idea was only named in 2022, and within four years it has gone from proposal to direct experimental confirmation. Days earlier, a separate team reported altermagnetism in a twisted two-dimensional structure, suggesting the hunt for new altermagnetic materials is already widening beyond MnTe.

I find the deeper point the most satisfying one. The two-category system survived for ninety years not because nature is tidy, but because our instruments could not see the twist. A better beamline, a sharper question about handedness, and a category that looked settled turns out to have been incomplete all along. That is a useful reminder for any field that feels finished: sometimes the third option is not a compromise between the first two. It is something genuinely new, hiding in the geometry.