Ultrathin Ruthenium Dioxide Films Reveal Altermagnetic Behavior

An international team of researchers has uncovered evidence that ruthenium dioxide displays altermagnetic behavior when prepared as an ultrathin film that is only a few atomic layers thick. The findings, which demonstrate that this unusual spin behavior appears under specific lattice strain conditions, have been officially published in Science Advances. The work highlights how material thickness and physical stress can fundamentally alter electronic properties.

Discussing the historical context of the material, Ming Yi from Rice University explained that ruthenium dioxide was originally one of the first materials proposed as an altermagnetic candidate. However, previous studies conducted on its bulk form failed to return any clear evidence of magnetism, leading scientists to traditionally consider bulk ruthenium dioxide as nonmagnetic. Expanding on this dichotomy, Ming Yi noted that their ongoing research shows that its ultrathin form may actually be the key factor in making the material magnetic.

Detailing the analytical process behind the discovery, Yichen Zhang stated that after analyzing their measurements and informing their interpretation with theoretical calculations, the team found that the ruthenium dioxide shows spin textures consistent with unconventional magnetism under experimental conditions. Yichen Zhang added that this suggests both bulk and ultrathin ruthenium dioxide may possess distinctly different magnetic properties when placed under the right conditions.

Exploring potential technological applications, Yichen Zhang pointed out that the strain-dependent nature of the material suggests scientists may be able to use lattice strain as a tuning knob to induce or control altermagnetism. According to Yichen Zhang, this capability could prove to be extremely useful when thinking about the development of next-generation spintronics and advanced RAM architectures in the future.

Addressing the complexity of the research, Ming Yi remarked that this work demonstrates just how intricate these scientific questions can be. Ming Yi emphasized that high-quality material preparation, performed by Bharat Jalan at the University of Minnesota, alongside careful measurement protocols executed by researchers including Milan Radovic from the Paul Scherrer Institute and Rachel Leeson, were critical to correctly observing the electron spin properties. The successful observation required a meticulous analysis of spin-resolved angle-resolved photoemission spectroscopy. Through this advanced method, the team was able to determine not only the magnetic state symmetries but also a potential way to manipulate the state in next-generation quantum materials.

The collaborative research effort involved multiple institutions, including Rice University, the University of Minnesota, and the Paul Scherrer Institute. Financial and structural support for the scientific undertaking was provided by organizations including ScienceDaily, the U.S. Department of Energy, the Gordon and Betty Moore Foundation, and the Robert A. Welch Foundation.