Dynamic pattern of Skyrmions observed

The illustration demonstrates skyrmions in one of their Eigen modes (clockwise).

The illustration demonstrates skyrmions in one of their Eigen modes (clockwise). © Yotta Kippe/HZB

Tiny magnetic vortices known as skyrmions form in certain magnetic materials, such as Cu2OSeO3. These skyrmions can be controlled by low-level electrical currents – which could facilitate more energy-efficient data processing. Now a team has succeeded in developing a new technique at the VEKMAG station of BESSY II for precisely measuring these vortices and observing their three different predicted characteristic oscillation modes (Eigen modes).

Cu2OSeO3 is a material with unusual magnetic properties. Magnetic spin vortices known as skyrmions are formed within a certain temperature range when in the presence of a small external magnetic field. Currently, moderately low temperatures of around 60 Kelvin (-213 degrees Celsius) are required to stabilise their phase, but it appears possible to shift this temperature range to room temperature. The exciting thing about skyrmions is that they can be set in motion and controlled very easily, thus offering new opportunities to reduce the energy required for data processing.

Three different Eigenmodes expected

Theoretical work had predicted that it should be possible to use a high-frequency electric field to  excite a group of skyrmions in the sample so that their cores will  rotate all together,  synchronously like a fish swarm, clockwise or counter-clockwise, or alternatively they can even exhibit a “breathing” motion.  Now a team has succeeded in measuring the dynamics of these skyrmions in detail using a single-crystal sample of Cu2OSeO3.

First experimental observation at VEKMAG

The team succeeded at BESSY II in combining a spin-resolving method with an external microwave field. „The resonant magnetic scattering technique when combined with magnetic vectorial external fields shows where the spins are located in the lattice and how they are oriented in space, and all these for each elemental spin species that may exist in the specimen“,  explains Dr. Florin Radu, at the Helmholtz-Zentrum Berlin (HZB),  a physicist who developed and set up the VEKMAG end station in cooperation with partners from the Universität Regensburg, Ruhr University Bochum, and Freie Universität Berlin. The construction and continuing development of the VEKMAG station are supported by the German Federal Ministry of Education and Research (BMBF) and HZB.

Using electric field induced ferromagnetic resonance excitation and recording the x-ray intensity  of a  so called Bragg peak, the research group demonstrated experimentally for the first time that all three characteristic oscillation modes occur in Cu2OSeO3 – the team observed magnetic skyrmions turning clockwise, counterclockwise, and expanding and contracting ("breathing" mode). Those modes can be switched and turned around by changing the frequency of the microwave field: Each dynamic mode is achieved for a certain frequency, which further depends on the external magnetic field as well as on other intrinsic parameters of the sample. “This is a first step towards phase specific characterization of controlled skyrmion’s gyrational motion”, Radu says.

Phys. Rev. Lett. (2019): Ferromagnetic Resonance with Magnetic Phase Selectivity by Means of Resonant Elastic X-Ray Scattering on a Chiral Magnet; S. Pöllath, A. Aqeel, A. Bauer, C. Luo, H. Ryll, F. Radu, C. Pfleiderer, G. Woltersdorf, and C. H. Back

DOI:    10.1103/PhysRevLett.123.167201

arö

You might also be interested in

  • Stability of perovskite solar cells reaches next milestone
    Science Highlight
    27.01.2023
    Stability of perovskite solar cells reaches next milestone
    Perovskite semiconductors promise highly efficient and low-cost solar cells. However, the semi-organic material is very sensitive to temperature differences, which can quickly lead to fatigue damage in normal outdoor use. Adding a dipolar polymer compound to the precursor perovskite solution helps to counteract this. This has now been shown in a study published in the journal Science by an international team led by Antonio Abate, HZB. The solar cells produced in this way achieve efficiencies of well above 24 %, which hardly drop under rapid temperature fluctuations between -60 and +80 Celsius over one hundred cycles. That corresponds to about one year of outdoor use.
  • HZB physicist appointed to Gangneung-Wonju National University, South Korea
    News
    25.01.2023
    HZB physicist appointed to Gangneung-Wonju National University, South Korea
    Since 2016, accelerator physicist Ji-Gwang Hwang has been working at HZB in the department of storage rings and beam physics. He has made important contributions to beam diagnostics in several projects at HZB. He is now returning to his home country, South Korea, having accepted a professorship in physics at Gangneung-Wonju National University.
  • Scientists Develop New Technique to Image Fluctuations in Materials
    Science Highlight
    18.01.2023
    Scientists Develop New Technique to Image Fluctuations in Materials
    A team of scientists, led by researchers from the Max Born Institute in Berlin and Helmholtz-Zentrum Berlin in Germany and from Brookhaven National Laboratory and the Massachusetts Institute of Technology in the United States has developed a revolutionary new method for capturing high-resolution images of fluctuations in materials at the nanoscale using powerful X-ray sources. The technique, which they call Coherent Correlation Imaging (CCI), allows for the creation of sharp, detailed movies without damaging the sample by excessive radiation. By using an algorithm to detect patterns in underexposed images, CCI opens paths to previously inaccessible information. The team demonstrated CCI on samples made of thin magnetic layers, and their results have been published in Nature.