A material thought to be nonmagnetic may reveal a hidden magnetic state when thinned to just a few atomic layers and placed under strain. (Artist’s concept.) Credit: SciTechDaily.com

A material once thought to be nonmagnetic may reveal a hidden magnetic side when made just a few atomic layers thick.

A newly proposed class of magnetism known as altermagnetism could open new possibilities for making computer memory smaller and more efficient. Now, researchers have found evidence that ruthenium dioxide, a quantum material long debated for its magnetic properties, may display this unusual form of magnetism when prepared as an ultrathin film only a few atomic layers thick.

The study was led by Rice University physicist Ming Yi, working with Bharat Jalan of the University of Minnesota and Milan Radovic of the Paul Scherrer Institute. Their findings were published in Science Advances.

“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.”

Measuring Magnetism at the Atomic Scale

To investigate the material’s magnetic behavior, the researchers examined the spin texture of ultrathin ruthenium dioxide. Spin texture describes how the magnetic moments associated with electrons are arranged throughout a material. By mapping those patterns, scientists can determine whether a material is magnetic and what kind of magnetism it may possess.

The team measured these electron spin patterns using spin-resolved angle-resolved photoemission spectroscopy, a technique that can reveal detailed information about the electronic and magnetic structure of a material.

“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 suggests that bulk and ultrathin ruthenium dioxide, under the right conditions, may have distinctly different magnetic properties.”

Illustration of strain-induced emergent magnetism in ultrathin RuO2/TiO2. Possible theoretic altermagnetic spin density is rendered with orange and blue visual effects in the top RuO2 layers using OpenAI ChatGPT. Credit: Rice University/Yichen Zhang

Strain May Act as a Magnetic Tuning Knob

A key factor was lattice strain, which places pressure on the electron structure of the ultrathin ruthenium dioxide. Under these strained conditions, the material produced spin patterns resembling those expected from altermagnetism.

Without that strain, including in the material’s natural bulk form, the researchers did not observe the same altermagnetism-like behavior.

“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 could be extremely useful when thinking about next-generation spintronics and RAM architectures.”

That possibility could be important for future electronic devices. If scientists can reliably control this magnetic state by adjusting strain, ultrathin quantum materials could offer new ways to manipulate electron spins in memory and spintronic technologies.

A Long-Running Debate Over Ruthenium Dioxide

The findings also highlight how difficult it can be to pin down the properties of quantum materials. Ruthenium dioxide has been at the center of a lengthy scientific debate as researchers tried to determine whether its bulk form is magnetic. The field eventually reached a general consensus that bulk ruthenium dioxide does not show magnetism.

The new results suggest that this picture may change when the same material is reduced to only a few atomic layers and placed under carefully controlled conditions.

“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 results required careful analysis of spin-resolved angle-resolved photoemission spectroscopy. Through this, we were able to determine not only the magnetic state symmetries but a potential way to manipulate it in next-generation quantum materials.”

Reference: “Observation of mirror-odd and mirror-even spin texture in ultrathin epitaxially strained RuO2 films” by Yichen Zhang, Seung Gyo Jeong, Luca Buiarelli, Seungjun Lee, Yucheng Guo, Jiaqin Wen, Hang Li, Sreejith Nair, In Hyeok Choi, Zheng Ren, Ziqin Yue, Jounghoon Hyun, Tieqiong Zhang, Alexei Fedorov, Sung-Kwan Mo, Hojoon Lim, Adrian Hunt, Iradwikanari Waluyo, Junichiro Kono, Ján Minár, Jong Seok Lee, Tony Low, Turan Birol, Rafael M. Fernandes, Milan Radovic, Bharat Jalan and Ming Yi, 29 July 2026, Science Advances.
DOI: 10.1126/sciadv.aec2917

The work was funded by the U.S. Department of Energy (DE-SC0026179, DE-SC0020211, DE-SC0024710), the Gordon and Betty Moore Foundation’s EPiQS Initiative (GBMF9470) and the Robert A. Welch Foundation (C-2175).

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