- Team uncovers surprising magnetic behaviour in ultra-thin layers of ruthenium dioxide (RuO2), a material conventionally characterised as metallic yet nonmagnetic.
By investigating one of the thinnest metallic oxide materials ever fabricated, the researchers at the University of Minnesota Twin Cities have uncovered surprising magnetic behaviour in ultra-thin layers of ruthenium dioxide (RuO2), a material conventionally characterised as metallic yet nonmagnetic.
The breakthrough holds promising implications, in the realm of spintronics and quantum computing, for the development of faster, smarter, and more energy-efficient electronic devices.
The cornerstone of this discovery lies in the innovative use of hybrid molecular beam epitaxy, an advanced materials growth technique that allows for the creation of atomically thin layers of RuO2.
By applying epitaxial strain—a process analogous to stretching or compressing a rubber band—the researchers induced magnetic properties in a material that typically exhibits none.
This epitaxial strain alters the internal atomic structure of RuO2 in such a precise manner that it transitions into an altermagnetic state, a novel class of magnetic behaviour hitherto observed in only a few materials.
Anomalous Hall effect
According to Professor Bharat Jalan, senior author of the study and Shell Chair holder at the University’s Department of Chemical Engineering and Materials Science, the metallic nature of RuO2 at the atomic scale is extraordinary.
“The material is described as the most metallic oxide known, with conductivity rivalling elemental metals and two-dimensional materials such as graphene. The manifestation of altermagnetism in ultra-thin RuO2 further elevates the material’s potential for technological integration.”
One particularly noteworthy magnetic phenomenon observed in this research is the anomalous Hall effect, whereby the path of electrical current is deflected in the presence of a magnetic field. Traditionally, achieving this effect in metallic RuO2 has necessitated the application of intense magnetic fields.
However, the team succeeded in eliciting this effect using much weaker fields in ultra-thin films, just two-unit cells thick—equivalent to less than a billionth of a meter. The retention of the material’s high metallicity and structural stability at such scales underscores its suitability for practical applications.
Strain engineering
The implications of this study extend beyond mere academic interest.
Seunnggyo Jeong, a postdoctoral researcher and first author on the paper, emphasised the practicality of the findings, noting that the material is compatible with real-world device integration.
“The potential impact on miniaturisation, speed enhancement, and energy efficiency is substantial, making this discovery highly relevant to the fields of artificial intelligence, low-power electronics, and next-generation memory devices.”
Furthermore, Professor Tony Low of the Department of Electrical and Computer Engineering highlighted the critical role of strain engineering in modulating material properties at the atomic scale.
“The approach paves the way for the deliberate design of materials with tailored magnetic and electronic behaviors, a vital step toward the realization of advanced platform materials for emerging quantum and spintronic technologies.”
Collaboration among scholars from the University of Minnesota, Massachusetts Institute of Technology, Gwangju Institute of Science and Technology, and Sungkyunkwan University enriched this research, illustrating the interdisciplinary and international nature of the endeavour.