Berlin 2024 – scientific programme

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MA: Fachverband Magnetismus

MA 30: Skyrmions II

MA 30.1: Invited Talk

Wednesday, March 20, 2024, 15:00–15:30, EB 301

Discovery of Hopfion rings in a cubic chiral magnet — •Nikolai Kiselev — Institute for Advanced Simulation and Peter Grünberg Institute, Forschungsyentrum Jülich, 52425 Jülich Germany

Magnetic skyrmions are two-dimensional topological solitons resembling vortex-like strings in the magnetization field that penetrate an entire sample. In contrast, hopfions are topological solitons localized in all three dimensions and manifest as closed loops of skyrmion strings, often taking the shape of a ring. While hopfions were theoretically predicted in specific magnetic systems [1], their direct observation has been elusive since, in most magnetic systems, isolated hopfions are unstable. Our discovery reveals that in crystals of cubic chiral magnets, hopfions become stable when linked with skyrmion strings [2]. This talk presents the direct observation of such hopfions in B20-type FeGe plates using transmission electron microscopy. Various aspects of hopfion rings will be discussed, including a reliable protocol for hopfion ring nucleation, a quantitative comparison between theory and experiment, a homotopy group analysis of these topological states, and an examination of zero modes of hopfion rings moving along skyrmion strings.

[1] Rybakov, F. N. et al. APL Mater. 10, 111113 (2022).

[2] Zheng, F. et al., Nature 623, 718 (2023).

Keywords: Hopfion; Skyrmion; Topological soliton; Chiral magnet; Electron microscopy