For generations, physics students have learned that magnets come in two families. In ferromagnets, like the ones holding drawings to a fridge, electron spins line up together and produce a field you can feel. In antiferromagnets, identified in the 1930s, neighbouring spins alternate up and down so their effects cancel. Now researchers headed by SLAC, the US national accelerator laboratory in California, report in the journal Science what it calls conclusive evidence for a third category: altermagnetism.
The name only dates back to 2022. It was coined for materials that look like antiferromagnets from the outside, with no overall magnetisation, yet behave in some ways like ferromagnets. The proposed explanation is geometric: the atomic cage around each up spin is turned at an angle compared with the cage around each down spin. By 2024 the evidence was mounting, but one key ingredient was still missing.
That ingredient was chirality, or handedness, the kind of twist found in a corkscrew or a spiral staircase. Lead author Daniel Jost and colleagues tested manganese telluride, a compound classed as an ordinary antiferromagnet for decades. At the ESRF synchrotron in Grenoble, France, they fired circularly polarised X-rays at samples, first twisting one way and then the other. The material responded differently to the two beams, a signal a conventional antiferromagnet should not produce.
The measurements were made in 2024 and repeated in early 2025 with the same outcome. Jost says the “chiral signature” gave the team firm ground to treat altermagnets as a class of their own.
The appeal for engineers is the combination. Altermagnets produce no stray fields that disturb nearby components, yet they could still carry information encoded in spin. That makes them candidates for faster memory, leaner data centres and quantum devices, although real products remain some way off.
