Modulation of Spin-Orbit Torque and Large Enhancement of Perpendicular Magnetic Anisotropy in W/Co20Fe60B20/MgO by Ir Insertion Layer

Iridium (Ir) is a 5d heavy metal with strong spin-orbit coupling (SOC), which introduces various intrigu-ing phenomena when interacting with a ferromagnetic layer. In this study, we utilize Ir as an insertion layer in W/Ir(tIr)/Co20Fe60B20/MgO heterostructures to tune SOC and study its influence on the spin-orbit torque (SOT), perpendicular magnetic anisotropy (PMA), and Dzyaloshinskii-Moriya interaction (DMI). The SOT efficiency decreases first and then increases with an increase of Ir insertion layer thickness because of the opposite spin Hall angle between W and Ir, and the sign changes when the thickness of Ir is 1.5 nm, which is close to the spin diffusion length of Ir of 1.35 nm. Importantly, a 0.25-nm-thick Ir layer enhances largely the effective PMA by 140%-350% under different annealing temperatures compared with that of a sample without insertion. Meanwhile, the DMI constant is also enhanced. The enhancement of PMA and DMI is likely due to the enhancement of interfacial SOC when Ir diffuses into Co20Fe60B20 and leads to the formation of Fe1-xIrx. These results provide an effective method to tune SOC by inducing a dusting layer with strong SOC to meet different requirements in spintronic devices like small magnetic tunnel junctions.