As the world generates more data than ever, scientists are searching for ways to store that information in smaller and more efficient formats. “As data volumes continue to grow, future magnetic storage media must be able to store information reliably at ever higher densities,” says Professor Jörg Wrachtrup, Head of the Center for Applied Quantum Technologies (ZAQuant) at the University of Stuttgart, whose team led the study. “Our results are therefore directly relevant for next-generation data storage technologies. At the same time, they are of fundamental importance, as they provide new insights into magnetic interactions in atomically thin materials.”
The international research group identified a previously unknown magnetic state in a material made of four atomic layers of chromium iodide. According to Dr. Ruoming Peng, a postdoctoral researcher at the 3rd Physics Institute of the University of Stuttgart, the team was able to fine tune the magnetism by adjusting how electrons interact within each layer. Peng conducted the experiments at ZAQuant alongside doctoral researcher King Cho Wong. “We can selectively control this magnetism by tuning the interactions between electrons in the individual layers,” Peng explains. “What is particularly remarkable is that the observed magnetic properties are robust against environmental perturbations.”
Twisted Two Dimensional Materials Create Skyrmions
Chromium iodide belongs to a category known as two-dimensional (2D) materials, which consist of only a few atomic layers arranged in a crystal structure. These ultra thin materials are known to behave very differently from their thicker, three-dimensional versions.
In this case, the researchers slightly rotated two stacked bilayers of chromium iodide relative to one another. That small twist produced an entirely new magnetic configuration. “In contrast, an untwisted bilayer does not exhibit a net external magnetic field, as shown in earlier studies,” says Peng. The rotation leads to the formation of skyrmions, which are nanoscale magnetic structures that are topologically protected and exceptionally stable. They rank among the smallest and most durable carriers of information known in magnetic systems. The team successfully generated and directly observed skyrmions in a twisted two-dimensional magnetic material for the first time.
Quantum Sensing Detects Extremely Weak Magnetism
Observing this new magnetic state was not straightforward because the signals involved are extremely faint. To measure them, the scientists relied on an advanced microscope that uses quantum sensing. This approach takes advantage of nitrogen-vacancy (NV) centers in diamond, a technique that has been developed and refined at the Center for Applied Quantum Technologies for more than twenty years.
Findings Challenge Existing Magnetic Theory
The discovery does more than suggest new possibilities for high density data storage. It also deepens scientific understanding of how electrons behave collectively in atomically thin magnetic systems. “Our experimental results indicate that existing theoretical models need to be refined to fully capture the observed phenomena,” says Wrachtrup.
The project brought together collaborators from the United Kingdom, Japan, the United States, and Canada in addition to the University of Stuttgart. Researchers at the University of Edinburgh led the theoretical modeling and numerical simulations.
About the Center for Applied Quantum Technologies
Research and teaching at the Center for Applied Quantum Technologies (ZAQuant) focus on solid-state quantum technology, with applications ranging from nanoscale quantum sensing to quantum networks. The institute’s infrastructure is a world-wide unique combination of precision as well as quantum optics laboratories and state-of-the-art cleanroom facilities.