Physicists have long classified magnetic materials as either ferromagnets or antiferromagnets. Now, researchers led by the U.S. Department of Energy’s SLAC National Accelerator Laboratory have reported experimental evidence for a proposed third class, known as alternating magnetism or altermagnetism. Their findings, based on measurements of manganese telluride, could eventually support advances in spin-based electronics, quantum devices and energy-efficient computing.
A third category of magnetic order
In a study published in Science, the research team presented evidence that alternating magnetism combines important properties traditionally associated with both ferromagnets and antiferromagnets.
“In recent years, scientists have observed phenomena that don’t fit neatly into the ferromagnetism/antiferromagnetism dichotomy,” said lead author Daniel Jost, an associate research scientist at SLAC and the Stanford Institute for Materials and Energy Sciences. “Researchers have compiled evidence for a third type of magnetism that bridges these two classes of properties. We believe our results provide solid experimental confirmation that this third step, alternating magnetism, is real.”
The researchers focused on manganese telluride, or MnTe, a material that was long classified as an antiferromagnet. Building on earlier work, they identified direct evidence of chirality: an asymmetry in the material’s magnetic structure. Chirality is similar to the directional twist of a spiral staircase or screw and is an important signature of alternating magnetism.
Beyond its importance to fundamental physics, the discovery could help researchers develop magnetic materials for advanced memory systems, quantum devices and more energy-efficient data centers.
How conventional magnetism works
Magnetism is familiar from everyday objects such as refrigerator magnets and compasses, but its atomic-scale origins are more complex.
At the atomic level, magnetism is related to a quantum property of electrons called spin. Spin does not mean that an electron literally rotates like a small ball, but it behaves in some ways like angular momentum. Scientists commonly describe the two possible spin orientations as “up” and “down.”
When electron spins form particular patterns, a material can exhibit magnetic properties. That does not necessarily mean that the material produces an externally detectable magnetic field.
In ferromagnets, electron spins align in the same direction, forming patterns such as up-up-up or down-down-down. Their combined effect produces the magnetic field associated with ordinary magnets. Humans have used materials with these properties for thousands of years.
Antiferromagnetism, identified as a distinct category in 1933, works differently. Neighboring electron spins point in opposite directions, creating an up-down-up-down pattern. Because the magnetic contributions cancel one another, the material has no overall magnetization.
How alternating magnetism differs
For nearly 90 years, ferromagnets and antiferromagnets provided the basic framework for understanding magnetic order in materials. More recent experiments, however, have revealed behaviors that do not fit completely into either category.
Some materials have alternating electron spins and no overall magnetization, like antiferromagnets. At the same time, they can support useful spin currents, a property associated with ferromagnets. Spin currents transfer information through the spin of electrons rather than relying entirely on their electric charge.
This combination suggested that the materials represented something fundamentally different. In 2022, researchers introduced the term “alternating current magnets” for materials belonging to this proposed third magnetic class.
The key difference is the arrangement of atoms in the crystal. Alternating magnets have opposing spin orientations, but the crystal structures surrounding those spins rotate relative to one another.
This rotation breaks a type of symmetry found in conventional antiferromagnets. Although the structural difference is subtle, it can significantly alter electron behavior, allowing alternating magnets to combine properties once thought to be mutually exclusive.
Chirality provides missing evidence
Although experimental support for alternating magnetism had been accumulating, researchers still needed decisive evidence that it represented a distinct magnetic phase.
“While there were several factors that strongly supported the realization of altermagnetism by 2024, there were still missing pieces of the puzzle,” Jost said.
One missing feature was chirality, sometimes described as “handedness.” An object is chiral when its mirror image does not exactly match the original. Human hands provide a familiar example: the left and right hands are mirror images, but a left hand does not fit correctly into a right-handed glove.
In alternating magnets, the unusual arrangement of atoms and electron spins can produce this handedness in the electronic and magnetic structure. Conventional antiferromagnets do not display the same characteristic chiral properties.
Detecting chirality could therefore distinguish genuine alternating magnets from materials that only appear to have similar properties.
The researchers selected manganese telluride as their test material. Although scientists had considered it an ordinary antiferromagnet for decades, more recent research raised the possibility that it belonged to the newly proposed category.
Polarized X-rays reveal a chiral response
To investigate the material, the team conducted experiments at the European Synchrotron Radiation Facility (ESRF) in France. The facility’s ID32 beamline produces precisely controlled polarized X-rays, enabling scientists to examine magnetic structures that are otherwise difficult to detect.
The researchers used circularly polarized X-rays whose electric field rotates either counterclockwise or clockwise as the light travels. By measuring how manganese telluride scattered the two forms of light, they searched for evidence of chirality.
“Chiral materials scatter left-polarized X-ray beams differently than right-polarized beams,” Jost explained. “Non-chiral materials scatter each ray of light the same way.”
The experiment found clear differences in how manganese telluride interacted with the two X-ray polarizations. This chiral response is expected for alternating magnetism and is absent from conventional antiferromagnets.
“This chiral feature gave us a solid experimental basis to say that altermagnetism is in a class of its own,” Jost said.
The researchers conducted their first experiment in 2024. They returned in early 2025 to repeat the measurements and reproduced the results, strengthening the evidence for a new magnetic phase.
“This technique helped confirm that manganese telluride indeed exhibits alternating magnetism,” said co-author Rachel Nickell, a postdoctoral fellow at ESRF who helped design and conduct the experiment at the ID32 beamline. “Although alternating magnetism was only proposed a few years ago, the rapid progress in confirming these models has been incredible.”
Potential applications in spintronics
The discovery could have implications for spintronics, a field that seeks to use electron spin to build higher-performance electronic devices.
Conventional electronics primarily store and process information by controlling the charge of electrons. Spintronics adds another method by manipulating electron spin.
This additional degree of control could allow devices to operate faster, resist interference more effectively and consume less power. Such improvements would be valuable for computer memory, large data centers and other systems that process vast amounts of information.
However, the two traditional types of magnetism pose different challenges for spintronic devices.
“Ferromagnetic materials are sensitive to magnetic fields,” Jost explained. “If you had a permanent magnet in your pocket and you walked by a spintronic device made of ferromagnets, the bits could start flipping and the information stored there could be scrambled. Antiferromagnets solve that problem, but they’re actually invisible, so the data stored there can’t be easily read or used to drive an efficient spin current.”
Alternating magnets could offer a compromise. Like antiferromagnets, their opposing spins produce no overall magnetization, helping protect them from unwanted magnetic interference. Their unusual electronic structure may also allow them to generate spin-polarized currents that can be used to retrieve information.
“Altermagnets combine the best of both worlds,” Jost said. “They are stable because they have zero net magnetization, but they also have the ability to generate the spin-polarized currents needed to easily extract information. This gives us even more freedom in our work.”
Future directions
Confirming alternating magnetism gives scientists a basis for studying new classes of materials and designing them for possible technological applications. By combining magnetic stability with the ability to manipulate spin-based information, these materials could help address limitations that have hindered traditional spintronic devices.
The next step is to learn how to control alternating magnetic states using external influences such as light or electricity. The researchers hope that controlling these states will eventually allow them to design practical devices that exploit the materials’ unusual properties.
Significant development remains necessary before alternating magnets can be widely used. For now, the discovery provides an experimental foundation for research into quantum technology, computer memory and more efficient data centers.
The research received partial funding from the DOE Office of Science.
Source: www.sciencedaily.com
