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Long-range chiral exchange interaction in synthetic antiferromagnets

Abstract

The exchange interaction governs static and dynamic magnetism. This fundamental interaction comes in two flavours—symmetric and antisymmetric. The symmetric interaction leads to ferro- and antiferromagnetism, and the antisymmetric interaction has attracted significant interest owing to its major role in promoting topologically non-trivial spin textures that promise fast, energy-efficient devices. So far, the antisymmetric exchange interaction has been found to be rather short ranged and limited to a single magnetic layer. Here we report a long-range antisymmetric interlayer exchange interaction in perpendicularly magnetized synthetic antiferromagnets with parallel and antiparallel magnetization alignments. Asymmetric hysteresis loops under an in-plane field reveal a unidirectional and chiral nature of this interaction, which results in canted magnetic structures. We explain our results by considering spin–orbit coupling combined with reduced symmetry in multilayers. Our discovery of a long-range chiral interaction provides an additional handle to engineer magnetic structures and could enable three-dimensional topological structures.

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The data sets generated during and/or analysed during the current study are available from the corresponding author on reasonable request.

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Acknowledgements

We acknowledge insightful discussions with M. Hoffmann, S. Blügel, B. Dupé and S.-B. Choe. We acknowledge F. Ummelen for personal discussions on her results that are relevant to this work. D.-S.H., K.L. and M.K. acknowledge support from MaHoJeRo (DAAD Spintronics network, project number 57334897) and the German Research Foundation (in particular SFB TRR 173 Spin+X). K.L. acknowledges the European Union’s Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie grant agreement Standard EF no. 709151. M.-H.J. acknowledges support from the National Research Foundation (NRF) of Korea grant funded by the Korea government (MEST) (nos 2017R1A2B3007918 and 2016M3A7B4910400). C.-Y.Y. acknowledges support from the NRF of South Korea under Grant 2017R1A2B3002621 and 2015M3D1A1070465, and J.-P.H. and Y.M. acknowledge computing time on the supercomputers JUQUEEN and JURECA at the Jülich Super-computing Center, and at the JARA-HPC cluster of RWTH Aachen, as well as funding under the SPP 2137 “Skyrmionics” (project MO 1731/7-1) and project MO 1731/5-1 of the Deutsche Forschungsgemeinschaft (DFG). D.-S.H. and K.-W.K. were supported by the Korea Institute of Science and Technology (KIST) institutional program (no. 2E29410) and a National Research Council of Science & Technology (NST) grant (no. CAP-16-01-KIST) funded by the Korea government (Ministry of Science and ICT). K.-W.K. acknowledges the DFG (no. SI 1720/2-1).

Author information

M.-H.J. and D.-S.H. conceived the original idea. D.-S.H., K.L., M.-H.J. and M.K. planned and designed the experiments. D.-S.H. and Y.V.H. fabricated the samples with R.L. and H.J.M.S. D.-S.H. and K.L. performed transport measurements with W.Y. and data analysis under the supervision of M.K. and M.-H.J. T.-W.K. provided [Pt/CoSiB]2/Pt multilayers. J.-P.H. and Y.M. performed the first-principles calculations and the analysis of relevant data. K.-W.K. provided theoretical explanations in Supplementary Information. D.-S.H. and C.-Y.Y. performed the numerical calculation based on a macrospin model. D.-S.H. wrote the paper with K.L., J.H. and M.K. All the authors discussed the results and commented on the manuscript.

Competing interests

The authors declare no competing interests.

Correspondence to Myung-Hwa Jung or Mathias Kläui.

Supplementary information

Supplementary Information

Supplementary Notes 1–5, Supplementary Figs. 1–9 and Supplementary references 1–13.

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Further reading

Fig. 1: Antisymmetric IEI in synthetic AFMs.
Fig. 2: Chiral and unidirectional magnetization switching behaviours.
Fig. 3: In-plane field dependence of magnetization switching fields.
Fig. 4: Effective symmetry breaking in sputtered samples and antisymmetric IEI from first principles.