Measuring Copper Selenate

Physicists at the TU Dresden, the Max Planck Institutes in Dresden and Stuttgart, and the Leibniz Institute for Solid State and Materials Research Dresden have now been able for the first time to gain a full understanding of magnetic interactions in copper selenate. In order to do so, they performed a series of inelastic neutron scattering experiments at three different neutron spectrometers at the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching and the Oak Ridge National Laboratory (ORNL, USA). The complete four-dimensional spectra were measured with the time-of-flight spectrometer at ORNL, whereas the three-axis spectrometers PUMA and PANDA in Garching were used to examine the essential details of the dispersion. The PANDA spectrometer is operated by the Jülich Centre for Neutron Science (JCNS).

Prof. Christian Pfleiderer and his group at the TU Munich discovered Skyrmions in metals experimentally in 2009. Since then, numerous researchers all over the world have also found these magnetic vortex structures in other materials. For this reason, they are of huge interest not only in basic research, but also because, unlike normal magnets, they theoretically offer great potential for magnetic data storage. Copper selenate is of particular interest as it is the first material that, despite not conducting an electric current, displays a very complex three-dimensional magnetic structure with a skyrmion lattice.

Intensity distribution in energy-momentum space during neutron scattering experiments using copper selenate.
Copyright: D. S. Inosov, TU Dresden

Magnetic vortex structures were first observed in copper selenates in 2012, and have since then been a source of fascination for theorists. The combination of different neutron methods has now made it possible to measure the complete spectrum of magnetic excitations. Thus the first experimental proof has been established that the different excitations in the spectrum are separated by a relatively large energy gap. The spectrum, now also quantitatively defined, indicates the exact positions of the energy gaps and makes it possible to calculate the magnetic interaction parameters. This constitutes an immense step forward in the understanding of skymions and thus towards the development of alternative magnetic systems for data storage.

Original publication:

P. Y. Portnichenko, J. Romhányi, Y. A. Onykiienko, A. Henschel, M. Schmidt, A. S. Cameron, M. A. Surmach, J. A. Lim, J. T. Park, A. Schneidewind, D. L. Abernathy, H. Rosner, Jeroen van den Brink, and D. S. Inosov;
Magnon spectrum of the helimagnetic insulator Cu₂OSeO₃,
Nature Communications 7, 10725 (2016)

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