Stack Structure Dependence of Co/Ni Multilayer for Current-Induced Domain Wall Motion

We developed a film stack structure of Co/Ni with perpendicular magnetic anisotropy (PMA), which is suitable for current-induced domain wall (DW) motion. A Ta/Pt underlayer effectively provided a sufficiently large PMA to achieve the DW motion driven by a small current. The critical current density ( j c ) had a minimum value at a Pt underlayer thickness ( t UL ) of 2.4 nm and was insensitive to cap layer thickness ( t cap ). The dependence of j c on t UL and t cap can be accounted for in terms of the effective spin polarization.