Processing effect on spin-orbit torque switching and efficiency characterization in perpendicularly magnetized pillar devices

Spin-orbit torque (SOT)-induced magnetization switching can be explained by either a single-domain coherent switching scenario or a domain-wall dynamics scenario, depending on the device size. In this study, we systematically investigate the processing effect on magnetic and SOT properties across a broad range of device sizes and geometries, from 5-mu m Hall bars to submicrometer-sized pillars and magnetic tunnel junctions (MTJs), with an identical W/CoFeB/MgO magnetic heterostructure. We first examine the impact of the fabrication process and device size on the measured magnetic properties, where coercivity H-c enhances while reducing the pillar size. Next, the current-driven hysteresis loop-shift measurement is utilized to characterize the dampinglike SOT efficiency xi(DL), which is found to be fairly size independent. In contrast, current-induced SOT switching shows that the critical switching current density J(sw) increases significantly with the device size reduction, suggesting a strong correlation between J(sw) and H-c. Nevertheless, the current-driven loop-shift phase diagram and the domain-wall depinning model provide a relatively consistent estimation of J(sw), verifying the applicability of these two methods in the studied pillar size range. Last, we compare the SOT switching results from a micrometer-sized Hall bar device and a micrometer-sized three-terminal MTJ device, where a consistent estimated dampinglike SOT efficiency can be reached. Our results give insight into the processing and size effects on magnetic devices and provide proper protocols for SOT efficiency and critical switching current density estimations.