SLAC researchers find proof of altermagnetism, a new magnetic phase

A SLAC-led team reports experimental evidence that altermagnetism is a distinct third phase of magnetism, beyond ferromagnetism and antiferromagnetism. Ferromagnets have aligned electron spins and produce a net magnetic field; antiferromagnets have alternating spins whose effects cancel. Altermagnets also have alternating spins, but the crystal structures around opposite spins are rotated relative to each other. This geometric twist may let them combine antiferromagnets’ lack of net magnetization with ferromagnets’ useful spin-related behavior. The category was proposed in 2022 to explain material properties that did not fit the two established types.

The missing evidence was chirality, or a distinct handedness in the magnetic and electronic structure, which conventional antiferromagnets should not show. Researchers tested manganese telluride (MnTe), long regarded as antiferromagnetic but recently identified as an altermagnet candidate. At the European Synchrotron Radiation Facility, they scattered circularly polarized X-rays from the material and compared its response to left- and right-handed beams. The differing responses revealed a clear chiral signal, supporting the conclusion that MnTe is altermagnetic. The team first conducted the experiment in 2024 and repeated it in early 2025, confirming the result. Identifying altermagnets could help researchers develop advanced electronics, including technologies for quantum applications, memory devices and data centers.