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Two-dimensional mutually synchronized spin Hall nano-oscillator arrays for neuromorphic computing

Abstract

In spin Hall nano-oscillators (SHNOs), pure spin currents drive local regions of magnetic films and nanostructures into auto-oscillating precession. If such regions are placed in close proximity to each other they can interact and may mutually synchronize. Here, we demonstrate robust mutual synchronization of two-dimensional SHNO arrays ranging from 2 × 2 to 8 × 8 nano-constrictions, observed both electrically and using micro-Brillouin light scattering microscopy. On short time scales, where the auto-oscillation linewidth \(\Delta f\) is governed by white noise, the signal quality factor, \(Q=f/\Delta f\), increases linearly with the number of mutually synchronized nano-constrictions (N), reaching 170,000 in the largest arrays. We also show that SHNO arrays exposed to two independently tuned microwave frequencies exhibit the same synchronization maps as can be used for neuromorphic vowel recognition. Our demonstrations may hence enable the use of SHNO arrays in two-dimensional oscillator networks for high-quality microwave signal generation and ultra-fast neuromorphic computing.

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Fig. 1: Schematic representation of a 4 × 4 SHNO array.
Fig. 2: PSD and micro-BLS microscopy of SHNO arrays.
Fig. 3: Linewidth, peak power and synchronization current density analysis of SHNO arrays.
Fig. 4: Neuromorphic computing with a 4 × 4 SHNO array.

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Data availability

The data that support the plots within this paper and other findings of this study are available from the corresponding author on reasonable request.

Code availability

The MATLAB codes used in this study are available from the corresponding author on reasonable request.

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Acknowledgements

This work was partially supported by the European Research Council (ERC) under the European Union’s Seventh Framework Programme (FP/2007-2013 ERC Grant no. 307144 ‘MUSTANG’) and Horizon 2020 research and innovation programme (ERC Advanced Grant no. 835068 ‘TOPSPIN’). This work was also partially supported by the Swedish Research Council (VR) and the Knut and Alice Wallenberg Foundation.

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Authors and Affiliations

Authors

Contributions

M.Z. designed and fabricated the devices, and carried out most of the electrical measurements and analysis of their microwave signal properties. A.A.A. and S.M. carried out all BLS measurements and analysis as well as the neuromorphic demonstration. R.K. and M.D. assisted with theoretical support and analysis. H.F. and H.M. assisted with microwave measurements and analysis. J.Å. coordinated and supervised the work. All authors contributed to the data analysis and co-wrote the manuscript.

Corresponding author

Correspondence to Johan Åkerman.

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The authors declare no competing interests.

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

Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Extended data

Extended Data Fig. 1 Linear micro-Brillouin Light Scattering microscopy profile along a row and a chain in a 4x4 SHNO array of 120 nm wide nano-constrictions separated by 300 nm.

(a) The power spectral density at H = 0.6 T and I = 7 mA, where four strong and stable modes are observed in the spectrum. To determine whether the partial synchronization is related to chains or rows we carried out Brillouin Light Scattering (BLS) microscopy line scans along both chains and rows. (b) A plot of the BLS counts and the frequency measured as a function of position along the red arrow shown in (c) reveals that the 4 oscillators are not operating at the same frequency. In contrast, (d) a similar scan along a chain as highlighted in (e) shows a constant BLS peak frequency independent of the position along the y-axis. This serves as conclusive proof that the oscillators first synchronise along each chain followed by the synchronization of all the chains together.

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Supplementary Information

Supplementary discussion and Figs. 1–4.

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Zahedinejad, M., Awad, A.A., Muralidhar, S. et al. Two-dimensional mutually synchronized spin Hall nano-oscillator arrays for neuromorphic computing. Nat. Nanotechnol. 15, 47–52 (2020). https://doi.org/10.1038/s41565-019-0593-9

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