Write Asymmetry of Spin-Orbit Torque Memory Induced by in-Plane Magnetic Fields

Write asymmetry, the significantly different write current for high-to-low and low-to-high resistance switching because of natural stochastic behaviors of magnetization, is a fundamental issue in magnetic random-access memory (MRAM). For high-performance spin transfer torque (STT) MRAM, it can be eliminated by precisely controlling atomically thin magnetic multilayers or by introducing compensation techniques in circuit-level designs, while for spin-orbit torque (SOT) MRAM, it has not been addressed. Here we systematically investigated the write asymmetry of SOT-MRAM as a function of applied magnetic fields (H) and demonstrated that the write currents are intrinsically asymmetric due to different SOT efficiencies for high-to-low and low-to-high switching. Furthermore, we found that the SOT efficiency is very sensitive to the tilt angle between H and write current, which can be tuned through H to achieve symmetric SOT switching. These results provide an additional guideline for designing SOT devices and suggest that the write asymmetry can be eliminated by adjusting the introduced effective magnetic fields within a field-free SOT-MRAM architecture.