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Towards control of the size and helicity of skyrmions in helimagnetic alloys by spin–orbit coupling

Nature Nanotechnology volume 8, pages 723–728 (2013)Cite this article

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Abstract

Chirality—that is, left- or right-handedness—is an important concept in a broad range of scientific areas. In condensed matter, chirality is found not only in molecular or crystal forms, but also in magnetic structures. A magnetic skyrmion1,2,3,4,5,6,7,8 is a topologically stable spin vortex structure, as observed in chiral-lattice helimagnets, and is one example of such a structure. The spin swirling direction (skyrmion helicity) should be closely related to the underlying lattice chirality via the relativistic spin–orbit coupling. Here, we report on the correlation between skyrmion helicity and crystal chirality in alloys of helimagnets Mn1−xFexGe with varying compositions by Lorentz transmission electron microscopy and convergent-beam electron diffraction over a broad range of compositions (x = 0.3–1.0). The skyrmion lattice constant shows non-monotonous variation with composition x, with a divergent behaviour around x = 0.8, where the correlation between magnetic helicity and crystal chirality changes sign. This originates from continuous variation of the spin–orbit coupling strength and its sign reversal in the metallic alloys as a function of x. Controllable spin–orbit coupling may offer a promising way to tune skyrmion size and helicity.

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Figure 1: Definitions of Γc and γm, and observation of skyrmions by Lorentz TEM.
Figure 2: Dependence of skyrmion size on x, obtained in a microcrystal of Mn1−xFexGe with varying composition (x ≈ 0.7).
Figure 3: Lorentz TEM images of magnetic helix and skyrmion, and CBED disk patterns used for determination of Γc.
Figure 4: Composition dependence of helical-magnetic properties of Mn1–xFexGe.

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Acknowledgements

The authors thank N. Nagaosa, S. Seki, T. Kurumaji and Y. Okamura for helpful discussions. This study was supported by a Grant-in-Aid for Scientific Research (grant no. 24224009) from MEXT, and by the Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST Program).

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Authors and Affiliations

  1. Department of Applied Physics and Quantum-Phase Electronics Center (QPEC), University of Tokyo, Tokyo, 113-8656, Japan

    K. Shibata, N. Kanazawa, S. Ishiwata & Y. Tokura

  2. RIKEN Center for Emergent Matter Science (CEMS), Wako, 351-0198, Japan

    X. Z. Yu, D. Morikawa & Y. Tokura

  3. Surface Physics and Structure Unit, National Institute for Materials Science, Tsukuba, 305-0044, Japan

    T. Hara, K. Kimoto & Y. Matsui

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  1. K. Shibata
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  5. N. Kanazawa
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Contributions

K.S. synthesized the polycrystalline samples, prepared the TEM samples, carried out the Lorentz TEM observations, and applied the CBED method. X.Z.Y. measured the EELS thickness map. T.H. measured the EDX composition map. D.M. analysed the CBED patterns. N.K. and S.I. contributed to the synthesis of polycrystalline samples. K.K. and Y.M. contributed to the EELS and EDX studies. Y.T. conceived the project and wrote the manuscript with K.S. and N.K.

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Correspondence to K. Shibata or Y. Tokura.

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Shibata, K., Yu, X., Hara, T. et al. Towards control of the size and helicity of skyrmions in helimagnetic alloys by spin–orbit coupling. Nature Nanotech 8, 723–728 (2013). https://doi.org/10.1038/nnano.2013.174

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