Efficient Manipulation of Magnetic Domain Wall by Dual Spin-Orbit Torque in Synthetic Antiferromagnets.

Current-induced domain-wall motion (CIDWM) in a synthetic antiferromagnet is a key phenomenon for developing potential high-density-packed magnetic domain-wall memory with fast operation. Here, CIDWM is reported in the antiferromagnetically-coupled two Co layers through the Ir interlayer sandwiched by the two Pt layers: Pt/Co/Ir/Co/Pt. The top and bottom Pt layers play a role for generating the spin current coming from the spin Hall effect, which gives rise to the dual spin-orbit torque (SOT) acting on the perpendicular magnetizations of the Co layers. Although a simple argument would predict that SOTs from top and bottom Pt layers cancel each other out, the dual SOT nucleates a reversed magnetic domain and drives the CIDWM effectively at current density of the order of 1011 A m-2. This study also examines the effect of antisymmetric interlayer exchange coupling (AIEC) on CIDWM. A positive correlation between the magnitude of AIEC and the domain wall velocity is found, whereas the current density required for nucleating the reversed domain shows a negative correlation with the magnitude of AIEC. These facts suggest that the existence of AIEC improves the performance of CIDWM. The present results provide a new avenue to design SOT domain wall devices based on a synthetic antiferromagnet.