The result adds an experimental chapter to a field that began with a theoretical proposal in 2022. Researchers used circularly polarized X-rays to detect a chiral magnetic excitation in manganese telluride, a material long treated as an antiferromagnet. The finding does not mean a new computer memory or low-power processor is ready to ship. It gives physicists a stronger basis for studying a magnetic state that may combine zero net magnetization with useful spin-dependent electronic behaviour.

A third category comes into focus

Magnetism is often introduced through two patterns. In a ferromagnet, many electron spins align in the same direction. Their contributions reinforce one another, creating net magnetization detectable outside the material. This is the principle behind an ordinary permanent magnet. In an antiferromagnet, neighbouring spins point in opposite directions. Their magnetic contributions largely cancel, so the material has no overall magnetization even though its microscopic magnetic order remains real. These are distinct arrangements of spin, not simply stronger and weaker versions of one state.

Altermagnetism pairs antiferromagnet-like cancellation with spin-dependent behaviour associated with ferromagnets. Opposite spins still form a compensated pattern, but crystal symmetries relating the spin sublattices allow electronic bands to split according to momentum. The material can have no net magnetic field while electrons moving through it still experience a direction-dependent spin structure. A 2022 paper in Physical Review X described this as a third distinct magnetic phase, giving a symmetry framework to phenomena that did not fit the older two-category picture.

Sources: SLAC researchers find proof of altermagnetism, a new magnetic phase · Emerging Research Landscape of Altermagnetism

Why manganese telluride became the test case

The material at the centre of the experiment is manganese telluride, or MnTe. For decades, it was classified as an antiferromagnet because its magnetic moments form an alternating arrangement with no net magnetization. Later work raised the possibility that its crystal and spin symmetries placed it in the altermagnetic class. The question is not whether MnTe is magnetic, but whether its ordered spins and electronic structure display the symmetry properties that define altermagnetism. The SLAC-led study built on earlier research rather than treating MnTe as an unknown substance.

In the altermagnetic description, opposite spin sublattices are related by a rotation of the crystal structure, unlike the symmetry relation in a conventional antiferromagnet. The resulting spin splitting depends on momentum and material symmetry. The 2022 framework set out how such a state could exist without a macroscopic magnetic moment. MnTe had already become a prominent candidate, so demonstrating a distinctive magnetic excitation in it offered a way to test the proposed picture against an observable signal.

Sources: SLAC researchers find proof of altermagnetism, a new magnetic phase · Chiral altermagnon in MnTe. · Emerging Research Landscape of Altermagnetism · Researchers find proof of altermagnetism, a new magnetic phase

The experiment looked for handedness

The team focused on chirality, or handedness. A chiral object cannot be perfectly superimposed on its mirror image: a left hand, for example, does not fit a right-handed glove. In a magnetic material, chirality can appear in the arrangement of spins and their collective excitations. The researchers worked at the European Synchrotron Radiation Facility in France, using its ID32 beamline for resonant inelastic X-ray scattering with circularly polarized light. The technique allowed them to probe magnetic excitations that are difficult to distinguish with ordinary measurements.

The key comparison was between the material’s response to left- and right-circularly polarized X-rays. In the experiment, the scattering response showed a chiral signature associated with a magnon in MnTe. A magnon is a collective wave-like excitation of ordered spins, rather than a single electron moving through a wire. The Science paper calls the observed mode a “chiral altermagnon”: its spin polarization changes with momentum in a way consistent with the g-wave symmetry expected for altermagnetic MnTe. That is more specific than simply seeing that the sample is magnetic.

Sources: SLAC researchers find proof of altermagnetism, a new magnetic phase · Chiral altermagnon in MnTe. · Researchers find proof of altermagnetism, a new magnetic phase · SLAC team confirms existence of third magnetic phase

What the Science paper establishes

The paper, titled “Chiral altermagnon in MnTe,” was published in Science on 29 October 2026. Its central result is direct experimental evidence for a chiral magnon in an altermagnetic candidate material, obtained through circular-dichroism resonant inelastic X-ray scattering. The authors report a distinct momentum dependence of spin polarization consistent with MnTe’s altermagnetic g-wave symmetry. They argue that the polarization-resolved measurements corroborate a discrete class of magnetic excitations and show how altermagnetic order shapes spin dynamics. The article is an experimental result, not a demonstration of finished technology.

Scientific confirmation usually comes through converging measurements, not one observation. SLAC says the first experiment was completed in 2024 and repeated in early 2025, reproducing the chiral signal. The repeated measurements strengthened the case that the result was not an isolated feature of one run. The paper lists researchers from SLAC, Stanford, Notre Dame, the European Synchrotron Radiation Facility and other institutions. SLAC says the work received partial support from the U.S. Department of Energy’s Office of Science.

Sources: SLAC researchers find proof of altermagnetism, a new magnetic phase · Chiral altermagnon in MnTe. · Researchers find proof of altermagnetism, a new magnetic phase · Research Roundup: Physicists discover new magnetic phase

Why spintronics is watching

Spintronics uses an electron’s spin as well as its electrical charge. Conventional electronics mainly move and control charge; spintronic devices seek to use the electron’s up-or-down spin state as another way to encode, carry or read information. Ferromagnets can provide strong spin polarization, but their net magnetization can make them vulnerable to stray magnetic fields. Antiferromagnets are less sensitive because their opposing spins cancel, yet their lack of net magnetization can make states harder to read and spin currents harder to use in some device designs.

Altermagnets may offer a route around part of that trade-off. Their compensated spin arrangement means zero net magnetization, while their symmetry can still support spin-polarized electronic states and currents. That combination could make them candidates for memory devices, quantum technologies and data-centre components. SLAC describes these as potential directions, not products validated by this experiment. The Science paper likewise points to spintronic and quantum technologies as areas the findings may help advance; it does not report a prototype memory chip or a measured reduction in computing power use.

Sources: SLAC researchers find proof of altermagnetism, a new magnetic phase · Chiral altermagnon in MnTe. · Researchers find proof of altermagnetism, a new magnetic phase · Research Roundup: Physicists discover new magnetic phase

A physics milestone, not a finished computer

The next stage is to learn how altermagnetic states can be controlled reliably. SLAC says future work will explore ways to influence them with light and electricity. That is an important step between identifying a magnetic phase and making it useful: a device would need to create, switch, preserve and read a chosen state repeatably. Researchers will also need to establish how the effects behave across different samples and device geometries. These are research questions raised by the path toward applications, not results delivered by the MnTe experiment.

The broader significance is substantial but carefully bounded. Altermagnetism gives condensed-matter physics a third symmetry-defined magnetic category and new spin dynamics to investigate. The MnTe measurements provide direct evidence for a chiral excitation consistent with that framework. Whether the material family can deliver faster memory, lower-energy computing or robust quantum components will depend on further materials research, control methods and engineering. For now, the achievement is a stronger experimental foundation: a once-theoretical magnetic phase has gained a measurable signature in a real material.

Sources: SLAC researchers find proof of altermagnetism, a new magnetic phase · Chiral altermagnon in MnTe. · Emerging Research Landscape of Altermagnetism · Researchers find proof of altermagnetism, a new magnetic phase · Research Roundup: Physicists discover new magnetic phase