Spin Hall effect induced SOT fields in perpendicular magnetized Co/Ni multilayer systems

Recently, Spin-Orbit torque (SOT) arising from the ferromagnetic heterostructures consisting of an ultra-thin ferromagnet (FM) sandwiched between a heavy metal (HM) and an Oxide layer has attracted extensive attention in the low power magnetic memory and logic devices. In this work, we characterized the SOT effective fields in Co/Ni multilayer systems with perpendicular magnetic anisotropy (PMA) using harmonic Hall voltage measurement technique. Compared to single thin FM, the multilayers have a higher plasticity in the thickness, which makes it more practical for real applications. Therefore the PMA stacks consisting of Ta/Pt/Ta/[Co/Ni]
_n
/Co/Ta/Ru were proposed. Normalized magnetization hysteresis loops were obtained using polar magneto-optical Kerr effect (MOKE) measurement technique.