Current-Induced Domain-Wall Motion for Electron Flow in Ferromagnetic Pt/Co/Ni/Co/Pt Wires

We report the current-induced domain-wall (CIDW) motion along the electron flow in the perpendicularly magnetized Co/Ni/Co structure sandwiched between the top and bottom Pt layers, observed by means of the Kerr microscope. As the lower Co thickness increases, the DW velocity for the electron flow is significantly increased, and also its motion becomes more stable irrespective of various current pulses. From the longitudinal field dependence of the DW velocity, it is found that the increase of the lower Co thickness increases a Dyzaloshinskii-Moriya interaction in the bottom Co/Pt interface, which results in the increase of the chiral spin torque, responsible for the increase of the DW velocity along the electron flow.