Field-Free Spin-Orbit Torque Switching of Co/Pd Memory Layer in CPP-GMR With Perpendicularly Magnetized SAF Pinned Layer

For the development of high-capacity spin-orbit torque (SOT) magnetic memory, a giant magnetoresistive (GMR) device with perpendicularly magnetized Co/Pd memory layer was fabricated, and current-induced magnetization reversal of the memory layer was investigated. A synthetic antiferromagnet (SAF) reference layer consisting of [Co/Pt]/Ru/[Co/Pt] multilayer (ML) was used for the GMR device to reduce the stray field in the pillar-shaped Co/Pd memory layer. Spin-transfer torque (STT) magnetization reversal of the memory layer and the field-assisted SOT magnetization reversal of the memory layer were confirmed by applying a current pulse through the GMR or through the bottom electrode, respectively. Furthermore, by injecting SOT and STT simultaneously, deterministic SOT switching of the perpendicularly magnetized Co/Pd memory layer was achieved in the absence of an in-plane-assisting magnetic field to break the symmetry. We confirmed that STT-assisting current significantly reduced the SOT switching current. Moreover, the assist efficiency defined by
$\Delta J_{\mathrm {SOT}} / \Delta J_{\mathrm {STT}}$
depended on the magnitude of in-plane magnetic field. Higher assist efficiency was obtained at lower in-plane magnetic field.