Direct observation and modeling of the plateau state in sub-nanosecond spin–orbit torque switching

Abstract

Spin–orbit torque (SOT) has attracted significant interest due to fast magnetization switching in next-generation spintronic devices. However, SOT-driven switching is hindered by a transient equilibrium state—termed a plateau—near the equator of the magnetization vector. Here, we experimentally observed the formation of this plateau using time-resolved magneto-optical Kerr effect measurements. The plateau persists during the current pulse due to the competition between damping-like and precessional torques. The time treach to reach this plateau sets a lower bound of pulse widths for deterministic switching. Micromagnetic simulations revealed a simple rule relating current density and in-plane magnetic field that governs treach. An empirical model based on the Landau–Lifshitz–Gilbert equation accurately reproduces these results, especially for treach below 100 ps. These findings provide practical guidelines for optimizing current pulse width in energy-efficient and high-speed SOT devices.