MINNEAPOLIS / ST. PAUL (06/16/2024) — In a new study, researchers at the University of Minnesota Twin Cities discovered surprising magnetic behavior in one of the thinnest metallic oxide materials ever made. This could pave the way for the next generation of faster and smarter spintronic and quantum computing devices.
The research is published in the Proceedings of the National Academy of Sciences of the United States of America (PNAS), a peer-reviewed, multidisciplinary, high-impact scientific journal.
Using an advanced materials growth technique—hybrid molecular beam epitaxy—the researchers created ultra-thin layers of RuO2, a compound typically known for its metallic but nonmagnetic behavior. By applying epitaxial strain to these atomically thin layers—similar to stretching or compressing a rubber band—they were able to induce magnetic properties in a material that is otherwise nonmagnetic.
"Our work shows that RuO2 is not just metallic at the atomic scale—it's the most metallic material we've observed in any oxide, rivaling even elemental metals and 2D materials, second only to graphene," said Bharat Jalan, the senior author of the study and a professor in the University of Minnesota's Department of Chemical Engineering and Materials Science and holds the Shell Chair. "What's 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."
One of the key magnetic effects observed is called the anomalous Hall effect, where electrical current bends in the presence of a magnetic field—an important feature for next-generation memory and data storage devices. Typically, this effect is hard to achieve in metallic RuO2 and requires extreme magnetic fields, but the researchers were able to observe it in ultra-thin RuO2 and with much weaker magnetic fields.
"It's exciting because this isn't just a laboratory curiosity—we're looking at a material that can be integrated into real devices," said Seunnggyo Jeong, a postdoctoral researcher in the Department of Chemical Engineering and Materials Science and first author on the paper. "This could have major implications for developing smaller, faster, and more energy-efficient technologies, directly relevant to artificial intelligence."
The researchers saw magnetic effects in films just two-unit cells thick—that's less than a billionth of a meter. And despite being so thin, the material remained highly metallic and structurally stable.
"This discovery shows how we can unlock completely new behaviors in materials just by controlling them at the atomic scale," said Tony Low, a professor in the Department of Electrical and Computer Engineering and co-author on the paper. "Our calculations confirmed that strain changes the internal structure of RuO2 in just the right way to make this altermagnetic behavior possible."
The team plans to continue exploring how combinations of strain and layering can be used to engineer new material properties. Their ultimate goal is to develop platform materials for future applications in quantum computing, spintronics and low-power electronics.
In addition to Jalan, Jeong, and Low, the University of Minnesota team included Zhifei Yang, Sreejith Nair, Rashmi Choudhary and Juhi Parikh from the Department of Chemical Engineering and Materials Science; along with Seungjun Lee from the Department of Electrical and Computer Engineering. This research was conducted in collaboration with Massachusetts Institute of Technology, Gwangju Institute of Science and Technology and Sungkyunkwan University.
This paper was funded by the U.S. Department of Energy, the Air Force Office of Scientific Research (AFOSR) and the University of Minnesota Materials Research Science and Engineering Center (MRSEC) . The work was completed in collaboration with the University of Minnesota Characterization Facility .
Read the full paper entitled, "Metallicity and Anomalous Hall Effect in Epitaxially-Strained, Atomically-thin RuO2 Films, on the PNAS website .
