Abstract
Magnetic skyrmions are topologically stable swirling spin textures that appear as particle-like objects in two-dimensional (2D) systems. Here, utilizing scalar magnetic X-ray tomography under applied magnetic fields, we report the direct visualization of the three-dimensional (3D) shape of individual skyrmion strings in the room-temperature skyrmion-hosting non-centrosymmetric compound Mn1.4Pt0.9Pd0.1Sn. Through the tomographic reconstruction of the 3D distribution of the [001] magnetization component on the basis of transmission images taken at various angles, we identify a skyrmion string running through the entire thickness of the sample, as well as various defect structures, such as the interrupted and Y-shaped strings. The observed point defect may represent the Bloch point serving as an emergent magnetic monopole, as proposed theoretically. Our tomographic approach with a tunable magnetic field paves the way for direct visualization of the structural dynamics of individual skyrmion strings in 3D space, which will contribute to a better understanding of the creation, annihilation and transfer of these topological objects.
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The data presented in the current study are available from the corresponding authors on reasonable request.
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Acknowledgements
The authors thank L. Peng, X. Z. Yu, N. Nagaosa, T. Arima and A. Kikkawa for enlightening discussions and experimental help. This work was partly supported by Grants-in-Aid for Scientific Research (grant nos. 18H03685, 18K14117, 20H00349, 21H04440, 21H04990, 21K18595, 21K13876) and Grant-in-Aid for Specially Promoted Research (15H05702) from JSPS, PRESTO (grant no. JPMJPR18L5, JPMJPR20B4) and CREST (grant no. JPMJCR1874) from JST, Asahi Glass Foundation and Murata Science Foundation. The synchrotron radiation experiments were performed with the approval of the Japan Synchrotron Radiation Research Institute (JASRI) (proposal nos. 2018A2067, 2019B1173 and 2020A2057).
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S.S., M.S. and T.O. planned the project. S.S., M.S., M.I. and T.O. performed the scalar magnetic X-ray tomography measurements. R.T., N.D.K., S.S., and Y.T. prepared the samples. M.I. and Y.S. supported the sample characterization. M.S. performed the reconstruction of the scalar magnetic tomography data. S.S. and M.S. analysed the reconstructed images and performed the simulation of tomographic reconstruction. K.S., S.S. and W.K. performed the theoretical calculations. S.S. wrote the manuscript with the support from M.S. and T.O. All authors discussed the results and commented on the manuscript.
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Supplementary Figs. 1–8 and Notes 1–9.
Supplementary Video 1
A series of XMCD images taken from various angles −90∘ ≤ θ ≤ 90∘ with 5∘ steps. The images taken at selected θ values are shown in Fig. 2 in the main text.
Supplementary Video 2
360∘ view of the experimentally reconstructed mc(r) profiles. The definition of background colour is the same as in Fig. 3b,c in the main text.
Supplementary Video 3
Slice animation of experimentally reconstructed mc(r) profiles, where the slice position is changed as a function of time. The selected slice images are shown in Fig. 3b,c in the main text.
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Seki, S., Suzuki, M., Ishibashi, M. et al. Direct visualization of the three-dimensional shape of skyrmion strings in a noncentrosymmetric magnet. Nat. Mater. 21, 181–187 (2022). https://doi.org/10.1038/s41563-021-01141-w
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DOI: https://doi.org/10.1038/s41563-021-01141-w
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