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Observation of two independent skyrmion phases in a chiral magnetic material

Abstract

Magnetic materials can host skyrmions, which are topologically non-trivial spin textures. In chiral magnets with cubic lattice symmetry, all previously observed skyrmion phases require thermal fluctuations to become thermodynamically stable in bulk materials, and therefore exist only at relatively high temperature, close to the helimagnetic transition temperature. Other stabilization mechanisms require a lowering of the cubic crystal symmetry. Here, we report the identification of a second skyrmion phase in Cu2OSeO3 at low temperature and in the presence of an applied magnetic field. The new skyrmion phase is thermodynamically disconnected from the well-known, nearly isotropic, high-temperature phase, and exists, in contrast, when the external magnetic field is oriented along the 〈100〉 crystal axis only. Theoretical modelling provides evidence that the stabilization mechanism is given by well-known cubic anisotropy terms, and accounts for an additional observation of metastable helices tilted away from the applied field. The identification of two distinct skyrmion phases in the same material and the generic character of the underlying mechanism suggest a new avenue for the discovery, design and manipulation of topological spin textures.

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Fig. 1: Qualitative depiction of the intensity patterns in reciprocal space characterizing the modulated magnetic order in Cu2OSeO3 and magnetic phase diagrams for different temperature versus field histories.
Fig. 2: Typical small-angle neutron scattering patterns, intensity maps, and specific temperature dependences of the integrated intensity for HFC/FH.
Fig. 3: Signatures of increasing magnetic anisotropies under increasing magnetic field at approximately 3.6 K and the skyrmionic nature of the low-temperature phase.
Fig. 4: Key results of the theoretical calculations.

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Acknowledgements

We wish to thank F. Haslbeck, S. Mayr, M. Meven and the team at FRM II for helpful discussions and support. A.C., M.H. and W.S. acknowledge financial support through the TUM Graduate School. L.H. and A.R. acknowledge financial support through DFG CRC1238 (project C02). M.G. acknowledges financial support from DFG CRC 1143 and DFG grant 1072/5. A.B., M.H., W.S. and C.P. acknowledge support through DFG TRR80 (projects E1, F2 and F7) as well as ERC-AdG (291079 TOPFIT).

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A.C., M.H., A.B., W.S. and S.M. performed the experimental work; A.C. analysed the data; C.P. supervised the experimental work; H.B. grew the single crystals; L.H., M.G. and A.R. developed the theoretical analysis; A.C. and C.P. proposed this study and wrote the manuscript; all authors discussed the data and commented on the manuscript; correspondence may be addressed to A.C. and C.P.

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Correspondence to A. Chacon or C. Pfleiderer.

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Supplementary figures S1 to S23

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Chacon, A., Heinen, L., Halder, M. et al. Observation of two independent skyrmion phases in a chiral magnetic material. Nature Phys 14, 936–941 (2018). https://doi.org/10.1038/s41567-018-0184-y

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