Rice researchers discover altermagnetism in ultrathin ruthenium dioxide films

A team of physicists at Rice University has found something unexpected hiding in an ultrathin slice of ruthenium dioxide: magnetism that shouldn't be there. The discovery, published in Science Advances, suggests that a material long thought to be non-magnetic in its natural form can actually display a newly identified type of magnetism when compressed into a film just a few atomic layers thick. The finding opens a door to manipulating quantum materials in ways that could reshape how computers store and process information.

Ruthenium dioxide has been a puzzle for years. Physicists proposed it as a candidate for a newly theorized class of magnetism called altermagnetism, but when they studied the material in its bulk form—the everyday version you might hold in your hand—they found no magnetic properties at all. The consensus settled: ruthenium dioxide was simply not magnetic. Ming Yi, an associate professor of physics and astronomy at Rice, and his collaborators Bharat Jalan from the University of Minnesota and Milan Radovic from the Paul Scherrer Institute decided to test whether the material might behave differently when made extremely thin.

To understand what was happening at the atomic level, the team measured the spin texture of their ultrathin ruthenium dioxide films. Spin texture is essentially a map of how the magnetic moments—the intrinsic angular momentum of electrons—arrange themselves in space. By using a sophisticated technique called spin-resolved angle-resolved photoemission spectroscopy, they could peer into the electron structure and see what was actually there. What they found was striking: the ultrathin form showed spin patterns consistent with altermagnetism, the very thing that had eluded researchers studying the bulk material.

But there was a catch. The magnetism only appeared under a specific condition: when the material was under lattice strain, a kind of physical pressure applied to its atomic structure. Without this strain, the ultrathin films behaved like their bulk counterparts—non-magnetic. Yichen Zhang, the paper's first author and a recent Rice graduate, realized this opened an unexpected possibility. If strain could turn magnetism on, then strain could potentially be used as a control mechanism, a tuning knob to switch altermagnetism on and off or adjust its strength.

This distinction between bulk and ultrathin forms reveals something deeper about how quantum materials work. The same material can have fundamentally different properties depending on how it's prepared and what conditions it's subjected to. For decades, physicists had debated what ruthenium dioxide's magnetic state actually was, and the answer turned out to be more nuanced than a simple yes or no. The material's behavior depends on its form and its environment.

The implications reach into the practical world of computing. Altermagnetism is being studied as a potential foundation for next-generation spintronics—technology that uses electron spin rather than just electrical charge to process information. Computer memory, particularly RAM, could be miniaturized and made more efficient if engineers could harness altermagnetism. The discovery that lattice strain can control whether altermagnetism appears in ruthenium dioxide suggests a pathway forward: engineers might be able to design quantum materials with specific magnetic properties by deliberately applying strain during fabrication.

Yi emphasized that the work required meticulous attention to detail. The quality of the material preparation mattered enormously, as did the precision of the measurement protocol. A less careful approach might have missed the signal entirely. The results also underscore how much remains to be understood about quantum materials. What appears settled in one form of a material can be overturned when that material is reshaped. As researchers push toward smaller, faster, more efficient devices, understanding these hidden properties becomes increasingly valuable.