Unusual metal oxide shows signs of magnetism under lattice strain in ultrathin layers

August 1, 2026 report Unusual metal oxide shows signs of magnetism under lattice strain in ultrathin layers Krystal Kasal Author Gaby Clark Scientific Editor Robert Egan Senior Editor Ruthenium dioxide (RuO2) is a metal oxide that commonly serves as an important metallic conductor, quantum material and industrial electrocatalyst. While there have been debates surrounding the magnetic properties of RuO2, it is generally thought to be nonmagnetic in its bulk form. But now, a new study, published in Science Advances, has found that very thin layers of RuO2 can become magnetic when its lattice is placed under strain. Ruthenium dioxide's uncertain magnetism RuO2 is known for its unusual magnetic properties, which have led some researchers to propose that it may be an altermagnet—a material with magnetic order but little or no overall magnetization. Most previous studies have examined bulk RuO2 crystals or thicker, relaxed films and have reported conflicting findings on magnetic order. Earlier studies linked RuO2 to magnetic order, unusual Hall effects and efficient spin-charge conversion, while later studies found no magnetic order in bulk or relaxed films. While one study reported the absence of altermagnetic properties down to 5 nanometers of RuO2 thickness, a fully strained ultrathin regime below about 4 nanometers had not been directly studied with both momentum and spin resolution. The authors of the new study write, "In particular, both experimental results and theoretical calculations suggest that epitaxial strain plays a crucial role in stabilizing the magnetic states of RuO2. Therefore, spectroscopy investigation with spin and momentum resolution to resolve the electronic band dispersion of ultrathin epitaxially strained RuO2 and its spin character is highly desired." Ultrathin material strain reveals new insights To test whether strain would induce magnetic properties in ultrathin RuO2, the team grew atomically smooth, fully strained 2-nanometer-thick RuO2 films on titanium dioxide-based substrates. They used spin-resolved, angle-resolved photoemission spectroscopy to measure electron energy, momentum and spin, and tested two measurement geometries to separate intrinsic spin textures from experimental artifacts. X-ray and optical measurements were then used to check film structure and symmetry. The team found that, in the strained RuO2 films, electrons showed an unusual momentum-dependent spin pattern. The patterns could not be explained by the film's nonmagnetic polar structure or by known measurement artifacts. This indicated to the team that intrinsic magnetic order was at play in the ultrathin strained films, strengthening the idea that strain might be used like a control knob to create new electronic and magnetic states in the film. The evidence was compatible with either weak ferromagnetism or altermagnetism. The study authors write, "A comprehensive symmetry analysis rules out nonmagnetic origins of this spin texture. These findings suggest an emergent nonrelativistic spin structure enabled by epitaxial strain in the ultrathin limit, marking a distinct departure from the behavior of relaxed or bulk RuO2." The tests were conducted at a temperature of around 15 kelvin, so the behavior at room temperature remains uncertain. But if found to be controllable in future studies, strain-engineered RuO2 could become a platform for low-power spintronic components that handle information through electron spin. These kinds of oxide heterostructures may offer an adjustable route to sensors, memory and other devices without relying on conventional ferromagnets. Written for you by our author Krystal Kasal, edited by Gaby Clark, and fact-checked and reviewed by Robert Egan—this article is the result of careful human work. We rely on readers like you to keep independent science journalism alive. If this reporting matters to you, please consider a donation (especially monthly). You'll get an ad-free account as a thank-you. Publication details Yichen Zhang et al, Observation of mirror-odd and mirror-even spin texture in ultrathin epitaxially strained RuO 2 films, Science Advances (2026). DOI: 10.1126/sciadv.aec2917 Journal information: Science Advances © 2026 Science X Network