Joint Seminar by IEEE Magnetics Society Distinguished Seminar Series and ECE Dept - Nanosecond Phase Ordering in an Ultra-Large Spin Hall Nano-Oscillator Lattice: Towards Ultra-Fast Ising Machines
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While mutually synchronized spin Hall nano-oscillators (SHNOs) [1] can be used for neuromorphic computing [2,3], the number of mutually synchronized SHNOs has remained limited to 50 in chains [4] and 64 in 2D arrays [2]. To synchronize larger arrays, one must increase the oscillator coupling strength, for example, by packing them more closely, which requires smaller SHNOs. Using enhanced spin-orbit torque, replacing W with a W88Ta12 alloy [5], we demonstrated 10 nm SHNOs operating at threshold currents as low as 26 μA [6]. We then fabricated very large SHNO arrays and found that we can synchronize over 100,000 SHNOs, operating at up to 34 GHz, with quality factors exceeding 10^6. [7] Time-resolved Brillouin Light Scattering microscopy reveals ordering times ranging from 10 to 50 ns, scaling logarithmically with the number of SHNOs, consistent with the Kuramoto model [8]. We have also demonstrated how we can control the sign and phase of the coupling between SHNOs using a combination of spin-wave-mediated coupling and voltage-controlled magnetic anisotropy [9]. Taken together, these results pave the way towards SHNO-based Ising machines [10].
Reference
[1] A. A. Awad et al., Nature Physics 13, 292 (2017).
[2] M. Zahedinejad et al., Nature Nanotechnology 15, 47 (2020).
[3] M. Zahedinejad et al., Nature Materials 21, 81 (2022).
[4] A. Kumar et al., Nano Letters 23, 6720 (2023).
[5] N. Behera et al., Phys. Rev. Appl. 18, 024017 (2022)
[6] N. Behera et al., Advanced Materials 36, 2305002 (2024)
[7] N. Behera et al., arXiv:2501.18321 (2025); Nature Nanotechnology, accepted.
[8] V. Flovik et al., Scientific Report 6, 32528 (2016).
[9] A. Kumar et al., Nature Physics 21, 245 (2025).
[10] A. Houshang et al., Phys. Rev. Appl. 17, 014003 (2022).
Prof. Johan Åkerman received his Ph.D. in Materials Physics from KTH Royal Institute of Technology in 1998. After a post-doc at the University of California, San Diego, he joined Motorola for four years to work on MRAM. In 2005, he returned to KTH in Sweden, and in 2008, he was recruited as Full Professor to the Physics Department at the University of Gothenburg. Since 2023, he is also a part-time Professor at Tohoku University, Sendai, Japan. He has worked on spintronic technology for the last 25 years, has authored over 350 scientific papers with more than 20,000 citations, and has founded three companies. His main projects are related to spin torque and spin Hall nano-oscillators, with particular focus on mutually synchronized oscillator networks for Ising machines and neuromorphic computing.