Storing ever-growing volumes of data in ever-smaller spaces
“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 group led the project. “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 team discovered a new magnetic state that emerges in a system consisting of four atomic layers of chromium iodide. “We can selectively control this magnetism by tuning the interactions between electrons in the individual layers,” explains Dr. Ruoming Peng, a postdoctoral researcher at the 3 rd Physics Institute of the University of Stuttgart, who carried out the experiments at ZAQuant together with doctoral researcher King Cho Wong. “What is particularly remarkable is that the observed magnetic properties are robust against environmental perturbations."
Unusual magnetic behavior in two-dimensional materials
The chromium iodide investigated in the study belongs to the class of two-dimensional (2D) materials — systems composed of only a few atomic layers arranged in a crystalline lattice. It has long been known that 2D materials can exhibit properties that differ fundamentally from those of their three-dimensional bulk counterparts.
By slightly twisting two bilayers of chromium iodide with respect to each other, the Stuttgart researchers created a novel magnetic state. “In contrast, an untwisted bilayer does not exhibit a net external magnetic field, as shown in earlier studies,” says Peng. The twisting gives rise to so-called skyrmions — nanoscale, topologically protected magnetic structures that are among the smallest and most stable information carriers known in magnetic systems. For the first time, the team succeeded in creating and directly detecting skyrmions in a twisted two-dimensional magnetic material.
Quantum sensing reveals weak magnetic signals
Detecting the new magnetic state posed a major experimental challenge, as the associated signals are extremely weak. To overcome this, the researchers employed a highly specialized microscope based on quantum sensing techniques. The method exploits nitrogen-vacancy (NV) centers in diamond, whose physical principles have been extensively developed and refined at the Center for Applied Quantum Technologies over the past two decades.
Theory must be refined
Beyond their technological relevance, the findings significantly advance the theoretical understanding of collective electron behavior 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.
In addition to the University of Stuttgart, research institutions from the United Kingdom, Japan, the United States, and Canada were involved in the project. The theoretical modeling and numerical simulations were led by researchers at the University of Edinburgh.
About ZAQuant
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.
Nature
Experimental study
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