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Spontaneous atomic-scale magnetic skyrmion lattice in two dimensions

Abstract

Skyrmions are topologically protected field configurations with particle-like properties that play an important role in various fields of science. Recently, skyrmions have been observed to be stabilized by an external magnetic field in bulk magnets. Here, we describe a two-dimensional square lattice of skyrmions on the atomic length scale as the magnetic ground state of a hexagonal Fe film of one-atomic-layer thickness on the Ir(111) surface. Using spin-polarized scanning tunnelling microscopy we can directly image this non-collinear spin texture in real space on the atomic scale and demonstrate that it is incommensurate to the underlying atomic lattice. With the aid of first-principles calculations, we develop a spin model on a discrete lattice that identifies the interplay of Heisenberg exchange, the four-spin and the Dzyaloshinskii–Moriya interaction as the microscopic origin of this magnetic state.

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Figure 1: The nanoskyrmion lattice of the Fe ML on Ir(111).
Figure 2: SP-STM measurements on the Fe ML on Ir(111).
Figure 3: Sketches of skyrmion and antiskyrmion spin structures.
Figure 4: Energy contributions to the nanoskyrmion lattice obtained within the extended Heisenberg model with parameters determined from first-principles calculations.
Figure 5: Tunnelling anisotropic magnetoresistance contrast.
Figure 6: Experimental proof of incommensurability, which shows that the nanoskyrmion lattice is detached from the underlying atomic lattice.

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Acknowledgements

S.H. thanks the Stifterverband für die Deutsche Wissenschaft for financial support. K.v.B., M.M., J.B., A.K. and R.W. thank the SFB668, the ERC Advanced Grant FURORE and the Landesexzellenzcluster Nanospintronics for financial support.

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Contributions

S.H. and G.B. carried out the density functional theory calculations and STM simulations and devised the spin model. K.v.B., M.M., J.B. and A.K. carried out the STM measurements. K.v.B. and M.M. analysed and interpreted the experimental data. S.H., K.v.B., G.B. and S.B. wrote the paper. All authors discussed the experimental and theoretical data and contributed to preparing the paper. S.H., K.v.B., M.M. and G.B. contributed equally to this work.

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Correspondence to Stefan Heinze or Kirsten von Bergmann.

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The authors declare no competing financial interests.

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Heinze, S., von Bergmann, K., Menzel, M. et al. Spontaneous atomic-scale magnetic skyrmion lattice in two dimensions. Nature Phys 7, 713–718 (2011). https://doi.org/10.1038/nphys2045

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