Seed Layer Effect on Memristive Behaviors of Trilayer Spin–Orbit Torque Device

Trilayer spin–orbit torque (SOT) memristors stand at the forefront of modern spintronics, integrating three distinct layers to exploit the synergistic effects of spin–orbit coupling and magnetic interactions. This paper investigates the memristivity of a trilayer SOT device that can be tuned by a seed layer (Ta or Cu) to alter the structural ordering of the bottom ferromagnetic channel of CoPt. A Cu seed layer mitigated the texture of CoPt (111) to enable multilevel SOT switching with stability exceeding that of a Ta seed layer. In experiments and micromagnetic simulations, the Cu seed was shown to enhance the resistance of the CoPt channel to fast Bloch-wall propagation, while reducing anisotropy to enable multilevel switching. The switching current required by Cu-seed devices was lower than that of Ta-seed devices, which can be attributed to higher SOT efficiency associated with spin-transfer ferromagnetic resonance. X-ray magnetic spectroscopy verified that the Cu seed layer enhanced spin–orbit coupling at the interface.