Spin–orbit torque induced magnetization switching in Pt/Co/Ta structures with perpendicular magnetic anisotropy

Abstract

Spin–orbit torque (SOT) induced magnetization switching is investigated in Pt/Co/Ta stacks with perpendicular magnetic anisotropy with the variation of the thickness of Ta layer (tTa). SOT is characterized by an effective spin Hall angle θSH, which is determined by an anomalous Hall resistance measurements method based on a macrospin model. A high charge current induced magnetization switching efficiency is achieved by the enhanced injection efficiency of spin currents from bottom Pt and top Ta with opposite signs of θSH. When tTa = 4 nm, the enhanced effective θSH for Pt/Co/Ta shows a maximum value around 0.356, which is larger than the sum of |θSH| for Pt and Ta and is ascribed to an additional interfacial SOT at Co/Ta interface. θSH gradually decreases with increasing Ta layer thickness beyond 4 nm, which can be explained by the improved crystallinity of Ta layer. Our results confirm a way to decrease the switching current density in SOT-based spintronic devices.