A recently proposed form of magnetism called altermagnetism could help scientists develop smaller, faster and more energy-efficient computer memory. Researchers have now found evidence that ruthenium dioxide, a quantum material previously considered nonmagnetic in bulk form, can display this unusual magnetic behavior when produced as ultrathin films only a few atomic layers thick.
Rice University physicist Ming Yi led the research in collaboration with Bharat Jalan of the University of Minnesota and Milan Radovic of the Paul Scherrer Institute. Their findings provide new insight into the magnetic properties of ultrathin ruthenium dioxide and the potential of altermagnetic materials for next-generation electronics.
“Ruthenium dioxide was one of the first materials proposed as a potential altermagnetic material, but studies of its bulk form found no evidence of magnetism,” said Yi, an associate professor of physics and astronomy. “Our study shows that reducing the material to an ultrathin form may be the key to inducing magnetic behavior.”
Detecting magnetism through electron spin
To investigate the magnetic state of ultrathin ruthenium dioxide, the researchers analyzed its spin organization. Spin texture describes how a material’s magnetic moments, or electron spins, are arranged throughout its structure. These patterns can reveal whether a material is magnetic and help identify the type of magnetism it exhibits.
The research team measured the spin patterns using spin-resolved angle-resolved photoelectron spectroscopy, an advanced technique that maps the electronic structure and spin properties of materials.
“After analyzing the measurements and using theoretical calculations to interpret the data, we found that ultrathin ruthenium dioxide exhibits a spin organization consistent with unconventional magnetism under the experimental conditions,” said Yichen Zhang, lead author of the study and a recent Rice University graduate. “This suggests that bulk and ultrathin ruthenium dioxide can have distinctly different magnetic properties when the material is prepared under the right conditions.”
Atomic strain may control magnetic properties
The researchers discovered that the unusual spin behavior appears only under specific conditions. In particular, the electronic structure of ultrathin ruthenium dioxide is affected by lattice distortion, which creates strain within the material’s atomic structure.
Without this strain, as in the material’s natural bulk form, the electron spins showed no evidence of altermagnetism.
“The strain-dependent behavior suggests that lattice strain could serve as a tuning mechanism for inducing or controlling altermagnetism,” Zhang said. “This could be especially valuable for next-generation spintronics and random-access memory technologies.”
The findings raise the possibility of deliberately engineering lattice strain to control the magnetic behavior of advanced electronic materials. Such control could benefit spintronics, a field that uses electron spin and electrical charge to process and store information, as well as the development of smaller, faster and more efficient computer memory.
Resolving the debate over ruthenium dioxide
The discovery also highlights the challenges involved in understanding quantum materials. Ruthenium dioxide has been the subject of a long-standing scientific debate, with physicists investigating whether its bulk form is magnetic. Researchers have ultimately agreed that bulk ruthenium dioxide does not exhibit conventional magnetism.
The new study suggests that changing a material’s dimensions and applying strain to its atomic structure can produce significantly different physical properties.
“This study demonstrates how complex these questions can be,” Yi said. “High-quality material preparation and carefully controlled measurements were essential for observing the precise electron spin properties. The results required detailed analysis using spin-resolved angle-resolved photoemission spectroscopy. This enabled us to determine not only the symmetry of the magnetic state but also potential ways to manipulate it in future quantum materials.”
This research was funded by the U.S. Department of Energy (DE-SC0026179, DE-SC0020211, DE-SC0024710), the EPiQS Initiative of the Gordon and Betty Moore Foundation (GBMF9470), and the Robert A. Welch Foundation (C-2175).
Source: www.sciencedaily.com