  To address thermal stability issues for spintronic devices with a reduced
size, we investigate spin-orbit torque in Co/Pt multilayers with strong
perpendicular magnetic anisotropy. Note that the spin-orbit torque arises from
the global imbalance of the spin currents from the top and bottom interfaces
for each Co layer. By inserting Ta or Cu layers to strengthen the top-down
asymmetry, the spin-orbit torque efficiency can be greatly modified without
compromised perpendicular magnetic anisotropy. Above all, the efficiency builds
up as the number of layers increases, realizing robust thermal stability and
high spin-orbit-torque efficiency simultaneously in the multilayers structure.

Materials Science;Mesoscale and Nanoscale Physics