Controlled transformation of skyrmions and antiskyrmions in a non-centrosymmetric magnet

Abstract

Control of topological spin textures in magnetic systems may enable future spintronic applications. Magnetic field pulses can switch the vortex polarity1 or the winding number of magnetic bubbles2. Thermal energy can reverse the helicity of skyrmions3 and induce the transformation between meron and skyrmion by modifying the in-plane anisotropy4,5. Among the various topological spin textures, skyrmions6,7 and antiskyrmions8,9,10 are nanometric spin-whirling structures carrying integer topological charges (N) of −1 and +1 (refs. 7,11,12), respectively, and can be observed in real space8,13. They exhibit different dynamical properties under current flow14,15,16,17,18, for example, opposite signs for the topological Hall effect. Here we observe, in real space, transformations among antiskyrmions, non-topological (NT) bubbles and skyrmions (with N of +1, 0 and −1, respectively) and their lattices in a non-centrosymmetric Heusler magnet, Mn1.4Pt0.9Pd0.1Sn, with D2d symmetry. Lorentz transmission electron microscopy images under out-of-plane magnetic fields show a square lattice of square-shaped antiskyrmions near the Curie temperature and a triangular lattice of elliptically deformed skyrmions with opposite helicities at lower temperatures. The clockwise and counter-clockwise helicities of the skyrmions originate from Dzyaloshinskii–Moriya interactions with opposite signs along the [100] and [010] directions, respectively. A variation of the in-plane magnetic field induces a topological transformation from antiskyrmions to NT-bubbles and to skyrmions, which is accompanied by a change of the lattice geometry. We also demonstrate control of the helicity of skyrmions by variations of the in-plane magnetic field. These results showcase the control of the topological nature of spin configurations in complex magnetic systems.

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Fig. 1: Square antiskyrmion lattice and an antiskyrmion-to-skyrmion transformation at room temperature in a Mn1.4Pt0.9Pd0.1Sn magnet with D2d symmetry.
Fig. 2: In-plane field-induced transformation between antiskyrmions and NT-bubbles at room temperature.
Fig. 3: In-plane field-induced changes of the symmetry of magnetic textures in a magnet with D2d symmetry.
Fig. 4: Control of the helicity of elliptically deformed skyrmions by the in-plane field at 250 K and a phase diagram observed in the MnPtPdSn thin plate.

Data availability

The data that support the findings of this study are available from the corresponding author upon reasonable request.

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Acknowledgements

We thank Y. Taguchi and M. Ishida for enlightening discussions and technical assistance, respectively. We thank T. Kikitsu and D. Hashizume (Materials Characterization Support Team in the RIKEN Center for Emergent Matter Science) for technical support on the TEM (JEM-2100F), which was used to obtain L-TEM images. This work was partly supported by Grants-in-Aid for Scientific Research (A) (grant no. 18H03685) and Grants-in-Aid for Scientific Research on Innovative Area ‘Nano Spin Conversion Science’ (grant no. 17H05186) from JSPS, PRESTO (grant no. JPMJPR18L5, JST) and CREST (grant no. JPMJCR1874, JST).

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Authors

Contributions

X.Y., S.S. and Y.T. jointly conceived the project. L.P., K.N. and X.Y. carried out L-TEM observations and analysed the experimental data. R.T. synthesized the MnPtPdSn crystals and performed magnetic property measurements. W.K., K.S., T.-H.A. and N.N. performed the simulations. L.P., X.Y., W.K., N.N., S.S. and Y.T. wrote the manuscript. All authors discussed the data and contributed to the manuscript.

Corresponding authors

Correspondence to Licong Peng or Xiuzhen Yu.

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The authors declare no competing interests.

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Peer review information Nature Nanotechnology thanks Lorenzo Camosi, Mathias Kläui and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Lattice forms of antiskyrmions simulated by using Landau–Lifshitz–Gilbert equation.

Simulated square lattice (a) and hexagonal lattice (b) of antiskyrmions with using the energies of the exchange energy (A), D2d-type DMI, Zeeman energy, uniaxial anisotropy energy (Ku), and demagnetization energy for a and the energies including A, DMI, and Zeeman energy for b, respectively. The colour wheel in b and the triangles in a-b indicate the direction of in-plane magnetizations of the magnetic textures, whereas the dark colour indicates out-of-plane magnetizations.

Extended Data Fig. 2 Simulated L-TEM images of antiskyrmion, NT-bubble, and skyrmion.

Magnetic textures (a, d, g), simulated (b, e, h) and experimental (c, f, i) L-TEM images of a-c square-shape antiskyrmion, d-f NT-bubble, and g-i elliptic skyrmion. The colour bar indicates the normalized components of out-of-plane magnetizations in magnetic textures.

Extended Data Fig. 3 Sequential L-TEM images during the transformation process between the square antiskyrmion lattice and the triangular NT-bubble lattice.

A series of L-TEM images with varying the in-plane field along a, \([0\bar 10]\) and [010], b, \([\bar 100]\) and [100] directions showing the transformation between antiskyrmion lattice and NT-bubble lattice through a mixed state of antiskyrmions and NT-bubbles in a reproducible way. The order of L-TEM observations is shown as the red arrows.

Extended Data Fig. 4 T-H phase diagram of various magnetic textures together with several L-TEM images observed in the (001) MnPtPdSn thin plate.

a, Phase diagram and L-TEM images of isolated antiskyrmions and skyrmions under the normal field. b, Phase diagram and L-TEM image of NT-bubbles under the tilting field with 15° relative to the \([00\bar 1]\) axis. Various phases of I,II, III, VI, VII and VIII have been described in the right panels of a, b. The field directions are indicated in the upper-right images of a, b. The open circles specify the (T, µ0H) points, where we have done the L-TEM observations.

Supplementary information

Supplementary Information

Supplementary Figs. 1–4 and Discussion.

Supplementary Video 1

Numerical simulation showing dynamics of skyrmion-to-NT-bubble transformation.

Supplementary Video 2

Numerical simulation showing dynamics of skyrmion-to-NT-bubble transformation.

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Peng, L., Takagi, R., Koshibae, W. et al. Controlled transformation of skyrmions and antiskyrmions in a non-centrosymmetric magnet. Nat. Nanotechnol. 15, 181–186 (2020). https://doi.org/10.1038/s41565-019-0616-6

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