Picosecond switching of magnetic tunnel junctions by spin-orbit torque

Ultrafast switching of magnetic tunnel junctions (MTJs) is essential for future high-bandwidth memory and in-memory computing. However, state-of-the-art electrical switching of MTJs remains constrained to hundreds of picoseconds, leaving a substantial gap between memory and processors. Here, we experimentally demonstrate field-free switching of three-terminal MTJs using picosecond electrical pulses driven by spin-orbit torque (SOT), surpassing the speed limit by an order of magnitude. We further use voltage-gated (VG) effect to probe SOT switching mechanisms over wide pulse-width ranges and identify a nonmonotonic VG-SOT efficiency. While the efficiency is pronounced under long-pulse excitation, it diminishes in the subnanosecond regime but reemerges as the pulse width scales down to 13.2 ps, yielding an energy consumption about 30 fJ per bit. Micromagnetic analysis reveals that, from dc to picosecond timescale, the dominant magnetization switching dynamics evolve from thermally activated reversal to incoherent precession to coherent precession. These results establish picosecond VG-SOT as a pathway toward ultrafast and energy-efficient memory and logic.