Ultrathin RuO2 shows strain-controlled
Researchers observed altermagnetism in strained ultrathin ruthenium dioxide films, a discovery that may advance spintronics and memory technology.
Scientists have found evidence that ruthenium dioxide, a material considered nonmagnetic in its bulk form, may display altermagnetism when prepared as an ultrathin film only a few atomic layers thick and placed under strain. The research, led by Rice University physicist Ming Yi with collaborators from the University of Minnesota and the Paul Scherrer Institute, was reported in Science Advances on August 27, 2026.
"Ruthenium dioxide was one of the first materials to be proposed as an altermagnetic candidate, but studies on its bulk form didn't return evidence of magnetism," said Yi, an associate professor of physics and astronomy. "Our research shows that its ultrathin form, on the other hand, may be the key in making it magnetic." The team's analysis of the material's spin texture suggests its magnetic properties differ distinctly from its bulk counterpart under the right conditions.
Detecting Magnetism Through Electron Spins
To investigate the magnetic state, the researchers examined the spin texture of ultrathin ruthenium dioxide. Spin texture describes how a material's magnetic moments, the spins of its electrons, are arranged in space. These patterns can reveal what kind of magnetism a material exhibits.
The team measured these patterns using spin-resolved angle-resolved photoemission spectroscopy. "After analyzing our measurements, including informing our interpretation with theoretical calculations, we found that, in our experimental conditions, the ruthenium dioxide shows spin textures consistent with unconventional magnetism," said Yichen Zhang, the first author on the paper and a recent Rice graduate. This points to a fundamental difference between the bulk and ultrathin forms of the material.
Atomic Strain as a Magnetic Control
The unusual spin behavior appeared under specific conditions. The electron structure of the ultrathin ruthenium dioxide had to experience lattice strain, which places pressure on the material's atomic structure. Without that strain, as in the material's natural bulk form, the electron spins did not show signs of altermagnetism.
"The strain-dependent nature suggests that we may be able to use lattice strain as a tuning knob to induce or control altermagnetism," Zhang said. This control could prove valuable for spintronics, a field that uses electron spin as well as electrical charge to process and store information, and for new computer memory designs. The result raises the possibility of deliberately adjusting lattice strain to control magnetic behavior in future electronic materials.
A Complex Quantum Material Debate
The findings highlight the difficulty in identifying the behavior of quantum materials. Ruthenium dioxide has been at the center of a lengthy scientific debate as physicists tried to determine whether its bulk form was magnetic. Researchers ultimately reached a consensus that bulk ruthenium dioxide does not exhibit magnetism.
The new work suggests that changing the material's dimensions and placing its atomic structure under strain can produce very different behavior. "This work shows just how complex these questions can be," Yi said. "The high quality material prep and the careful measurement protocol were critical to our observation of the correct electron spin properties." The team's analysis of spin-resolved angle-resolved photoemission spectroscopy allowed them to determine magnetic state symmetries and a potential way to manipulate it. This 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.
