Practical design rules for easy-axis engineering in field-free in-plane SOT-MRAM cells

Abstract

Easy-axis canting is an effective strategy for achieving field-free switching in in-plane spin–orbit torque (SOT) magnetic tunnel junctions. However, the practical design rules for selecting the canted angle under realistic device layouts and operating conditions remain unclear. Here, we present a layout-aware micromagnetic study that systematically maps the dependence of switching efficiency, write current, and power consumption on the easy-axis canted angle (φ) and pulse duration (τ) in in-plane SOT devices. By explicitly incorporating the φ-dependent current-path geometry extracted from device layouts, we demonstrate that the angles minimizing the critical current density, write current, and power are generally distinct. For large devices, the optimal canted angles are well defined and largely insensitive to pulse duration and aspect ratio. In contrast, aggressive lateral scaling leads to strong pulse width-driven migration of the optimal angle, such that no single φ simultaneously optimizes all metrics. Under ultrashort pulses, the optimal angle is further modulated by the field-like torque, which stabilizes intermediate-angle configurations. These results establish the canted angle as a geometry-, pulse-, and metric-dependent design variable, providing practical guidance for angular selection in scalable, field-free, in-plane SOT-MRAM (magnetoresistive random access memory) cells.