Ruthenium dioxide has long puzzled physicists. In its normal, bulk form, the material is definitively nonmagnetic — a question settled by decades of experiments. But a new study from Rice University and the University of Minnesota shows that when ruthenium dioxide is made into an ultrathin film only a few atomic layers thick, something unexpected happens: it becomes magnetic.
Not just any magnetism, but altermagnetism — a recently proposed third class of magnetic behavior that falls between ferromagnetism (where electron spins all point the same way) and antiferromagnetism (where they cancel out). Altermagnetism, first theorized in 2019 and experimentally demonstrated in 2024, combines features of both, potentially enabling computer memory that is smaller, faster, and more energy-efficient than anything available today.
The findings, published August 27 in Science Advances, were led by Ming Yi, an associate professor of physics at Rice University, along with Bharat Jalan of the University of Minnesota and Milan Radovic of the Paul Scherrer Institute.
The team examined ruthenium dioxide's "spin texture" — the spatial arrangement of electron magnetic moments — using a technique called spin-resolved angle-resolved photoemission spectroscopy. What they found was a pattern consistent with altermagnetism: an unconventional magnetic state that had never before been observed in this material.
The key ingredient was strain. When the ultrathin ruthenium dioxide film was grown under conditions that compressed or stretched its atomic lattice, the material's electrons developed spin patterns characteristic of altermagnetism. Without that strain, the spins showed no magnetic order — confirming that strain, not just thickness, controls the transition.
"The strain-dependent nature suggests that we may be able to use lattice strain as a tuning knob to induce or control altermagnetism," said Yichen Zhang, the study's first author and a recent Rice graduate. "This could be extremely useful when thinking about next-generation spintronics and RAM architectures."
The result is significant because altermagnetism, if it can be reliably controlled, could provide a foundation for magnetic memory technologies that are both denser and faster than current designs. Spintronic devices — which use electron spin as well as electrical charge to process and store information — could benefit from materials whose magnetic properties can be switched on and off with precision.
The work also resolves a longstanding debate over ruthenium dioxide's magnetic character. After years of conflicting experimental results, the scientific community had reached a consensus that the bulk form was nonmagnetic. This new research shows that dimensional reduction and strain can fundamentally alter a material's magnetic identity — a lesson that may apply to other quantum materials as well.
The research was funded by the U.S. Department of Energy, the Gordon and Betty Moore Foundation's EPiQS Initiative, and the Robert A. Welch Foundation.
