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Symmetry-dependent field-free switching of perpendicular magnetization

Nature Nanotechnology volume 16, pages 277–282 (2021)Cite this article

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Abstract

Modern magnetic-memory technology requires all-electric control of perpendicular magnetization with low energy consumption. While spin–orbit torque (SOT) in heavy metal/ferromagnet (HM/FM) heterostructures1,2,3,4,5 holds promise for applications in magnetic random access memory, until today, it has been limited to the in-plane direction. Such in-plane torque can switch perpendicular magnetization only deterministically with the help of additional symmetry breaking, for example, through the application of an external magnetic field2,4, an interlayer/exchange coupling6,7,8,9 or an asymmetric design10,11,12,13,14. Instead, an out-of-plane SOT15 could directly switch perpendicular magnetization. Here we observe an out-of-plane SOT in an HM/FM bilayer of L11-ordered CuPt/CoPt and demonstrate field-free switching of the perpendicular magnetization of the CoPt layer. The low-symmetry point group (3m1) at the CuPt/CoPt interface gives rise to this spin torque, hereinafter referred to as 3m torque, which strongly depends on the relative orientation of the current flow and the crystal symmetry. We observe a three-fold angular dependence in both the field-free switching and the current-induced out-of-plane effective field. Because of the intrinsic nature of the 3m torque, the field-free switching in CuPt/CoPt shows good endurance in cycling experiments. Experiments involving a wide variety of SOT bilayers with low-symmetry point groups16,17 at the interface may reveal further unconventional spin torques in the future.

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Fig. 1: Crystal structure and symmetry analysis.
Fig. 2: Symmetry-dependent field-free magnetization switching.
Fig. 3: Symmetry dependence of current-induced effective fields.
Fig. 4: Theoretical model for current-induced spin torque in the CuPt/CoPt bilayer.
Fig. 5: Current-induced field-free magnetization switching in CuPt (13 nm)/CoPt (4 nm) pillar sample.

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Data availability

The authors declare that the main data supporting the findings of this study are available within the Letter and its Supplementary Information. Extra data are available from the corresponding author upon reasonable request. Source data are provided with this paper.

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Acknowledgements

This research is supported by the Singapore National Research Foundation under CRP Award No. NRF-CRP10-2012-02 and the Singapore Ministry of Education MOE2018-T2-1-019 and MOE2018-T2-2-043, A*STAR Grant No. A1983C0036, A*STAR IAF-ICP 11801E0036, MOE Tier1 R-284-000-195-114 and the King Abdullah University of Science and Technology (KAUST). J.S.C. is a member of the Singapore Spintronics Consortium (SG-SPIN).

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  1. These authors contributed equally: Liang Liu, Chenghang Zhou.

Authors and Affiliations

  1. Department of Materials Science and Engineering, National University of Singapore, Singapore, Singapore

    Liang Liu, Chenghang Zhou, Xinyu Shu, Changjian Li, Tieyang Zhao, Weinan Lin, Jinyu Deng, Qidong Xie, Shaohai Chen, Jing Zhou, Rui Guo, Han Wang, Jihang Yu, Shu Shi, Ping Yang, Stephen Pennycook & Jingsheng Chen

  2. Singapore Synchrotron Light Source (SSLS), National University of Singapore, Singapore, Singapore

    Ping Yang

  3. Physical Sciences and Engineering, King Abdullah University of Science and Technology, Thuwal, Saudi Arabia

    Aurelien Manchon

  4. Aix-Marseille Univ, CNRS, CINaM, Marseille, France

    Aurelien Manchon

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Contributions

L.L. and J.S.C. conceived and designed the experiments. L.L. and C.Z. performed the thin film deposition, device fabrication, transport measurements and data analysis. A.M. theoretically proposed the 3m torque and performed the calculations. T.Z., X.S., J.D., Q.X., S.C., S.S. and J.Y. contributed to the thin film deposition and device fabrication. W.L., J.Z., R.G., H.W. and P.Y. contributed to the data analysis. C.L. and S.P. performed the STEM experiments. L.L., C.Z., A.M. and J.S.C. wrote the manuscript and all authors contributed to its final version.

Corresponding authors

Correspondence to Aurelien Manchon or Jingsheng Chen.

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The authors declare no competing interests.

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Peer review information Nature Nanotechnology thanks Byong-Guk Park and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Sections 1–14, Figs. 1–38 and refs. 1–4.

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Source Data Fig. 3

Numerical data.

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Liu, L., Zhou, C., Shu, X. et al. Symmetry-dependent field-free switching of perpendicular magnetization. Nat. Nanotechnol. 16, 277–282 (2021). https://doi.org/10.1038/s41565-020-00826-8

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