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Experimental observation of chiral magnetic bobbers in B20-type FeGe

Abstract

Chiral magnetic skyrmions1,2 are nanoscale vortex-like spin textures that form in the presence of an applied magnetic field in ferromagnets that support the Dzyaloshinskii–Moriya interaction (DMI) because of strong spin–orbit coupling and broken inversion symmetry of the crystal3,4. In sharp contrast to other systems5,6 that allow for the formation of a variety of two-dimensional (2D) skyrmions, in chiral magnets the presence of the DMI commonly prevents the stability and coexistence of topological excitations of different types7. Recently, a new type of localized particle-like object—the chiral bobber (ChB)—was predicted theoretically in such materials8. However, its existence has not yet been verified experimentally. Here, we report the direct observation of ChBs in thin films of B20-type FeGe by means of quantitative off-axis electron holography (EH). We identify the part of the temperature–magnetic field phase diagram in which ChBs exist and distinguish two mechanisms for their nucleation. Furthermore, we show that ChBs are able to coexist with skyrmions over a wide range of parameters, which suggests their possible practical applications in novel magnetic solid-state memory devices, in which a stream of binary data bits can be encoded by a sequence of skyrmions and bobbers.

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Fig. 1: ChBs and SkTs in a nanostripe.
Fig. 2: Experimental evidence for the nucleation of chiral magnetic bobbers by means of in-field cooling.
Fig. 3: Nucleation of a ChB from an edge dislocation in the helical state in an inclined external magnetic field.
Fig. 4: Stability of chiral magnetic bobbers in different fields and temperatures.

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Acknowledgements

This work was supported by the National Key R&D Program of China, grant no. 2017YFA0303201, the Natural Science Foundation of China, grant nos 51622105 and 11474290, the Key Research Program of Frontier Sciences, CAS, grant no. QYZDB-SSW-SLH009, the Key Research Program of the Chinese Academy of Science, grant no. KJZD-SW-M01, the Major/Innovative Program of Development Foundation of Hefei Center for Physical Science and Technology, grant no. 2016FXCX001 and the Youth Innovation Promotion Association CAS no. 2015267. F.Z. and R.E.D.-B. acknowledge the European Union for funding through the Marie Curie Initial Training Network SIMDALEE2. The research leading to these results has received funding from the European Research Council under the European Union’s Seventh Framework Programmer (FP7/2007–2013)/ERC grant agreement no. 320832. The work of F.N.R. was supported by the Swedish Research Council grant no. 642-2013-7837. The work of A.B.B. was carried out within the state assignment of FASO of Russia (theme Quantum no. 01201463332).

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N.S.K. and H.D. contributed to the planning of this study. F.N.R. proposed the concept and, together with A.B.B., performed the preliminary simulations. F.Z. together with D.S., S.W., N.S.K. and H.D. performed the experiments. H.D., A.K. and R.E.D.-B. supervised and designed the experiments. N.S.K. performed the micromagnetic simulations and prepared the initial version of the manuscript. J.C. calculated the theoretical phase-shift images. F.N.R., M.T., S.B. and R.E.D.-B. edited the manuscript. All of the authors discussed the results and contributed to the preparation of the manuscript.

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Correspondence to Haifeng Du or Nikolai S. Kiselev.

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Supplementary Figures 1–11, Supplementary Table 1, Supplementary references.

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Zheng, F., Rybakov, F.N., Borisov, A.B. et al. Experimental observation of chiral magnetic bobbers in B20-type FeGe. Nature Nanotech 13, 451–455 (2018). https://doi.org/10.1038/s41565-018-0093-3

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