Whirlwind in Matter: Dresden Physicist

image: 3D volume representation of the magnetic field of skyrmion tubes inside a sample of FeGe. The direction of the magnetic field is color coded and indicated throughout the volume. In the cross section of the sample, the magnetic field is further represented by arrows. The distance between two tubes is about 100 nm.
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Credit: Daniel Wolf

The revolutionary novelty of the success of the Dresden search: Until now, there were only two-dimensional images of these objects, called skyrmions, either on the material surface or in the form of a projection. However, this meant that the depth resolution was completely lost and therefore it was not possible, for example, to distinguish between what was in front and what was behind. The spatial representation that has now become possible is a milestone in the field of nanomagnetism and “spintronics”, where skyrmions could replace bits and bytes as data storage units in the future.

Still, the underlying experiment of the Dresden research team could only be carried out at the Ernst Ruska Center in Jülich in February 2020 with great luck. Indeed, immediately afterwards, the research center was closed to external experiments for a long time due to the Corona pandemic. “When we then evaluated the data obtained in Dresden, our joy was immense. We had in fact succeeded in making the magnetic field of these vortices visible in three dimensions. Today we receive inquiries about this from all over the world” , reports Dr. Lubk, who is currently a group leader at IFW.

Skyrmions – Hype in Information Technology

Until now, information is stored and processed mainly on a semiconductor basis, i.e. via a flow of electrons. But electronic systems are limited in their performance. The search for alternatives occupies research and industry worldwide, and attention is increasingly focused on optical and magnetic information processing, the latter known as spintronics. The reason for the hype around magnetic vortices, skyrmions: with their help, data could be transported in the future in an extremely energy-efficient and space-saving way. Tiny skyrmions, ranging in size from ten to one hundred nanometers, are among the topological quantum phenomena being researched in the ct.qmat center of excellence. They are extremely stable and can be easily handled.

“Until now, the scientific community only had a two-dimensional image of skyrmions, which offer great potential for storing and processing large amounts of information. The three-dimensional image is a real milestone for the physics of the For the first time, we were able to see how curved these vortices are and how they influence each other,” comments Prof. Matthias Vojta, Dresden spokesperson for the ct.qmat cluster of excellence .

The history of Dresden’s pioneering achievement

In 2006, magnetic skyrmions were theoretically predicted. In 2009, they could be detected experimentally for the first time indirectly. In 2010, the first direct two-dimensional imaging was performed. Dr. Lubk’s research team has now succeeded for the first time in imaging the three-dimensional magnetic field of skyrmions with a resolution of a few nanometers. To this end, the team studied iron germanium (FeGe) using tomographic methods in a transmission electron microscope.

“The biggest challenge in our research project was the experimental frame. We spent five months developing a support for the sample so that it could rotate 360 ​​degrees. In the end, it was only thanks to a combination of different methods and technical advances we were able to see that nanovortices are actually tubes,” Dr. Lubk said. “Skyrmion tubes move like vortices in the material, and when another vortex gets too close to them, they switch.” The research was published in the journal Nature Nanotechnology in March 2022. In May 2022, the team of authors received the 2021 Outstanding Paper Award for Materials Science from the EMS for their three-dimensional imaging of the magnetic structure of skyrmion tubes, identification of their structural details and measurement of their energy density.

Outlook

The breakthrough involved Dresden researchers from the ct.qmat cluster of excellence, IFW Dresden, TU Dresden and the Max Planck Institute for Chemical Physics of Complex Systems. The experiment was conducted by Dr. Daniel Wolf (IFW) at the Forschungszentrum Jülich. The special specimen assembly, which made tomographic images possible in the first place, was developed by Dr. Sebastian Schneider (TU Dresden).

After the three-dimensional imaging and characterization of the skyrmionic tubes, the Dresden research team focuses on the analysis of other 3D nanomagnetic phenomena and the search for materials in which the magnetic vortices are generated at room temperature and without a magnetic field. external. At the same time, the researchers are working on the further development of the experimental device in order to make the method accessible to the global scientific community.

Best Paper Award
The EMS (European Microscopy Society) awards the Outstanding Paper Award each year in three categories. A jury selects the most important publication in the field of microscopy. The prize is endowed with 1,000 euros and was awarded this year in May at the PICO conference in Jülich.

Center of Excellence ct.qmat
The center of excellence ct.qmat–Complexity and Topology in Quantum Matter is a joint research collaboration between Julius-Maximilians-Universität Würzburg and Technische Universität (TU) Dresden since 2019. More than 270 scientists from 34 countries and four continents carry out research on topological quantum materials that reveal surprising phenomena under extreme conditions such as high temperatures, high pressures or strong magnetic fields. The cluster of excellence is funded within the framework of the excellence strategy of the federal and state governments, as the only cluster in Germany that crosses the borders of the federal states.

Publication
Daniel Wolf, Sebastian Schneider, Ulrich K. Rößler, András Kovács, Marcus Schmidt, Rafal E. Dunin-Borkowski, Bernd Büchner, Bernd Rellinghaus and Axel Lubk, Unveiling the Three-Dimensional Magnetic Texture of Skyrmion Tubes, Nature Nanotechnology 17 (2022) 250 –255. https://doi.org/10.1038/s41565-021-01031-x


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