European team develops Unified theory for skyrmion-materials
More than six years ago, physicists at the Technische Universität Muenchen discovered extremely stable magnetic vortex structures in a metallic alloy of manganese and silicon. Since then, they have driven this technology further together with theoretical physicists from the University of Cologne.
Since magnetic vortices are microscopic and easy to move, computer chips made with this technology would need 10,000 times less electricity than today's and store much larger amounts of data. Recent research results showed that the unique electromagnetic properties of skyrmions could also be used for the construction of efficient and very small microwave receivers and transmitters.
Conductors, semiconductors and insulators
The production of computer chips requires insulating, semiconducting and conducting materials. Today, magnetic vortex structures are available for all these three classes of materials. An important advantage is that these vortices respond easily to alternating fields so that information can be processed at high rates.
Now a team of physicists at the TU Muenchen, the University of Cologne and the à‰cole Polytechnique Fédérale de Lausanne (Switzerland) has examined the dynamic behavior of the insulator MnSi, the compound semiconductor Fe1-xCoxSi and the conductor Cu2OSeO3.
With the results of their measurements, the team have developed a theoretical description of behaviour valid for all three material classes. "With this theory, we have laid an important foundation for further developments," says Dirk Grundler, Chair of Physics of Functional Multilayers at the TU Muenchen. "In the future, we will therefore be able to identify materials with the specific properties we need for functional devices."
Extremely compact frequency devices
The typical resonance frequencies of the skyrmions are in the microwave range - the frequency range of mobile phones, Wi-Fi and many types of microelectronic remote controls. Thanks to the robustness of the magnetic vortices and their ease of excitability, skyrmion-materials could be the basis for highly efficient microwave transmitters and receivers.
While the wavelength of electromagnetic microwaves typically lies in the range of centimetres, the wavelengths of the magnetic spin waves, so-called magnons, are 10,000 times shorter. "In the area of microelectronics, much more compact or even entirely new devices could be developed from magnetic nanomaterials such as the skyrmion-materials," says Grundler.
In addition to the material itself, its shape also significantly influences the electromagnetic properties of the device. Here, too, the researchers' newly developed theory is very useful. It can predict which form produces the best properties for which material.
"Chiral magnetic materials promise a lot of new functionalities with an interesting interplay of electronic and magnetic properties," says Dr. Markus Garst, a physicist at the Institute for Theoretical Physics at the University of Cologne. "But for all applications, it is essential to predict the possibilities and limitations of various materials. We have come a big step closer to achieving this goal."
The work was funded by the European Research Council (ERC Advanced Grant), the Deutsche Forschungsgemeinschaft (TRR 80, SFB 608 and Nanosystems Initiative Munich, NIM) as well as the TUM Graduate School.
"˜Universal helimagnon and skyrmion excitations in metallic, semiconducting and insulating chiral magnets' by T. Schwarze et al, Nature materials (2015) DOI: 10.1038/nmat4223
