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Direct observation and dynamics of spontaneous skyrmion-like magnetic domains in a ferromagnet

Abstract

The structure and dynamics of submicrometre magnetic domains are the main factors determining the physical properties of magnetic materials1,2. Here, we report the first observation of skyrmion-like magnetic nanodomains in a ferromagnetic manganite, La0.5Ba0.5MnO3, using Lorentz transmission electron microscopy (LTEM). The skyrmion-like magnetic domains appear as clusters above the Curie temperature. We found that the repeated reversal of magnetic chirality is caused by thermal fluctuation. The closely spaced clusters exhibit dynamic coupling, and the repeated magnetization reversal becomes fully synchronized with the same chirality. Quantitative analysis of such dynamics was performed by LTEM to directly determine the barrier energy for the magnetization reversal of skyrmion-like nanometre domains. This study is expected to pave the way for further investigation of the unresolved nature and dynamics of magnetic vortex-like nanodomains.

a, Magnetization curve under B = 0.1 T. b, Temperature dependence of the domain structure of the zero-field state. Images were obtained using the underfocused Fresnel method. To obtain clear contrasts, the defocus value was changed depending on temperature (Δf = −0.1 mm at 100 K, −0.12 mm at 230 K, −0.2 mm at 270 K and −0.3 mm at 310 K). The alternating array of bright and dark lines, indicated by arrowheads, corresponds to FM domain walls. Red arrows indicate the remaining magnetic clusters. c, Fresnel image (Δ = −0.4 mm) of clusters of various sizes and shapes at 300 K. Blue arrows indicate peanut-shaped and analogous clusters.

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Figure 2: Analysis of spin structure of a cluster.
Figure 3: Skyrmion dynamics.
Figure 4: Analysis of dynamics of a single skyrmion.

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Acknowledgements

The authors thank T. Nagai and X. Z. Yu for helpful discussions, and W. Z. Zhang and Y. Hara for technical support during TEM experiments. This study was partly supported by the Nanotechnology Network Project and Nanotechnology Platform Project, MEXT, Japan.

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Contributions

M.N. designed the research, carried out the LTEM observations and TIE analysis, interpreted the data, prepared the sample, and wrote the paper. Y.G.S., K.I. and K.K. contributed to the discussion and wrote part of the manuscript. H.Y. contributed to the magnetization measurement and prepared the sample. H.Y., M.I. and T.H. contributed to the discussion.

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Correspondence to Masahiro Nagao.

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The authors declare no competing financial interests.

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Nagao, M., So, YG., Yoshida, H. et al. Direct observation and dynamics of spontaneous skyrmion-like magnetic domains in a ferromagnet. Nature Nanotech 8, 325–328 (2013). https://doi.org/10.1038/nnano.2013.69

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