Enhancement of spin hall effect-induced torques for current-driven magnetic domain wall motion: Extrinsic spin hall effect

The current-induced domain wall motion (CIDM) in thin perpendicular magnetized ferromagnetic wires sandwiched between a heavy metal and an oxide has been expected to be very efficient in getting high DW velocity at low current density for developing spintronic devices [1-3]. The addressed high velocity in these asymmetric wires is attributed to the presence of structural inversion asymmetry (SIA) and/or heavy metals like Pt which can lead to strong spin-orbit interaction (SOI) and induce additional spin-orbit torques (SOTs). Recently, a transition from bulk to interfa-cial effect is confirmed as a change in the DW motion direction at a reduced layer thickness of Co/ Ni multilayer down to 2.1 nm [4]. As discussed in Ref. [4], the adiabatic spin-transfer torque (STT) dominates the DW motion in the thick regime, while the interfacial torque due to the spin Hall effect (SHE) induces DW motion in the thin regime. In an earlier study [5], however, we can still observe the SOTs-induced DW motion up to a thickness of ∼ 10 nm for the asymmetric interfacial wire with the layered structure of SiO 2 /[Tb(3.2 A)/Co(2.6 A)] n /Pt(20 A). The high efficiency of SOTs in our wires can be explained by an addition of the extrinsic SHE from Co ultrathin layers due to Tb rare-earth impurity-induced skew scattering in the Co layer with the aid of SOI [6,7]. In this study, we present the current-induced DW motion in the Tb/Co wires with different layered structures. The extrinsic SHE is tuned by changing the thickness of Co ultrathin layers, number of Tb/Co interfaces, and formation of Tb-Co alloy magnetic layer.