DATE2021.12.01 #Press Releases

New Control Method for Topological Spin Crystals Discovered

Disclaimer: machine translated by DeepL which may contain errors.

-Pioneering New Magnetic Vortex Crystals and Conduction Properties by Phase Change of Spin Waves-.

The University of Tokyo

Japan Science and Technology Agency

Summary

Ken Hayami, Lecturer, Department of Science, Graduate School of Engineering, The University of Tokyo, Takeshi Okubo, Associate Professor, Corporate Sponsored Research Program in Quantum Software, Graduate School of Science, The University of Tokyo, and Yukitoshi Motomu, Professor, Department of Physics of Engineering, Graduate School of Engineering, The University of Tokyo, and their colleagues have focused on the phase in the superposition of spin waves as a new control variable in geometrically spin textured topological spin crystals and theoretically discovered a new topological spin crystal and a microscopic mechanism of topological phase transition phenomena caused by the phase change in the superposition of spin waves as a new control variable in topological spin crystals with geometric spin texture.

Recently, topological spin crystals, which appear when electron spins in solids form vortex structures, have attracted much attention. This phenomenon is expected to be applied to new devices with high-speed, high-efficiency, and energy-saving performance because the magnetic structure is protected by topological properties and a huge electromagnetic response appears, which is difficult to realize in ordinary magnetic materials. Up to now, magnetic skyrmion crystals and magnetic hedgehog crystals have been vigorously investigated as topological spin crystals, but new types of topological spin crystals have been desired in order to expand the possibilities of application.

By focusing on the phase in the superposition of spin waves that constitute topological spin crystals and theoretically investigating its role, this research group has discovered a new type of magnetic vortex crystal with a geometric spin texture different from that of magnetic skyrmion crystals. Furthermore, by performing large-scale numerical simulations on a theoretical model of magnetic metals, we have clarified the microscopic mechanism that switches the obtained magnetic vortex crystals and magnetic skillmion crystals. The results of this research are expected to lead to the construction of a scientific theory toward a new topological materials science based on the phase control of spin waves.

The research results were published in the online edition of the British scientific journal Nature Communications on December 1, 2021 (UK time).

Figure: Topological phase transition brought about by the phase change of spin waves
As shown in the figure above, completely different patterns (interference fringes) can be obtained by shifting the phase of the superposition of waves. The figure below shows an example of phase shift in a topological spin crystal (top panel: spin array, bottom panel: physical quantities related to the emergent electromagnetic field produced by the geometric spin texture). The left panel represents a magnetic skyrmion crystal with a topological number of 2, and the right panel represents a new magnetic vortex crystal obtained in this study. The topological phase transition between them is induced by changes in temperature, Fermi surface geometry, and spin-spin interactions.

For more information, please visit the website of the Faculty of Engineering , The University of Tokyo.