RuO2 is renowned for its metallic but nonmagnetic properties. However, the team were able to produce magnetic characteristics in the material by applying epitaxial strain to these atomically thin layers. This process is analogous to stretching or compressing a rubber band.
Our work shows that RuO2 is not just metallic at the atomic scale, it is the most metallic material we have observed in any oxide, rivaling even elemental metals and 2D materials, second only to graphene. What is more exciting is that this is one of the first experimental demonstrations of an altermagnetic state in ultra-thin RuO2, a new and exciting class of magnetic material.
Bharat Jalan, Study Senior Author and Professor, Department of Chemical Engineering and Materials Science, University of Minnesota
One key magnetic effect observed in the study was the anomalous Hall effect. This occurs when an electrical current bends in the presence of a magnetic field and is a critical characteristic for next-generation memory and data storage systems.
This effect is usually difficult to generate in metallic RuO2 and needs strong magnetic fields, but in the ultra-thin RuO2 produced in this study, the electrical effect was seen and with significantly weaker magnetic fields.
It is exciting because this is not just a laboratory curiosity, we are looking at a material that can be integrated into real devices. This could have major implications for developing smaller, faster, and more energy-efficient technologies, directly relevant to artificial intelligence.
Seunnggyo Jeong, Study First Author and Postdoctoral Researcher, Department of Chemical Engineering and Materials Science, University of Minnesota
The researchers saw magnetic effects even in films that were only two unit cells thick—less than a billionth of a meter. And, in spite of its thinness, the material showed significant metallic content and structural integrity.
This discovery shows how we can unlock completely new behaviors in materials just by controlling them at the atomic scale. Our calculations confirmed that strain changes the internal structure of RuO2 in just the right way to make this altermagnetic behavior possible.
Tony Low, Study Co-Author and Professor, Department of Electrical and Computer Engineering, University of Minnesota
The researchers intend to continue investigating how strain and layering might be utilized to manufacture novel material properties. Their goal is to create platform materials for future applications in quantum computing, spintronics, and low-power devices.
Journal Reference:
Jeong, S. G., et al. (2025) Metallicity and anomalous Hall effect in epitaxially strained, atomically thin RuO2 films. PNAS. doi.org/10.1073/pnas.2500831122.