Reinforcement-Learning-Designed Field-Free Sub-Nanosecond Spin-Orbit-Torque Switching

Yuta Igarashi; Junji Fujimoto

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arXiv · 2508.10792

Reinforcement-Learning-Designed Field-Free Sub-Nanosecond Spin-Orbit-Torque Switching

Yuta Igarashi·Junji Fujimoto

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Abstract

We demonstrate deterministic, field-free magnetization reversal of a single-domain nanomagnet within 300 ps under a current density of $3 \times 10^{10}~\mathrm{A/m^2}$ by coupling reinforcement learning (RL) to the Landau-Lifshitz-Gilbert equation with the spin-orbit torques (SOTs). The RL agent autonomously discovers a current waveform that minimizes the magnetization trajectory path and exploits a precessional shortcut enabled by the field-like SOT and hard-axis anisotropy. From the learned pulse, we extract a clear physical picture of the dynamics and develop a model-based analytical framework that establishes a lower bound on the switching time. The control strategy remains robust across a wide range of damping constants and is stabilized against thermal fluctuations at higher current densities. We also discuss feasible experimental implementations for the precessional switching.

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Yuta Igarashi, Junji Fujimoto. 2025-08-14. Reinforcement-Learning-Designed Field-Free Sub-Nanosecond Spin-Orbit-Torque Switching. https://arxiv.org/abs/2508.10792

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