Modulation of Spin-Orbit Torque and Large Enhancement of Perpendicular Magnetic Anisotropy in W/Co20Fe60B

Iridium ($\mathrm{Ir}$) is a 5d heavy metal with strong spin-orbit coupling (SOC), which introduces various intriguing phenomena when interacting with a ferromagnetic layer. In this study, we utilize $\mathrm{Ir}$ as an insertion layer in $\mathrm{W}/\mathrm{Ir}({t}_{\mathrm{Ir}})/{\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}/\mathrm{Mg}\mathrm{O}$ 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 $\mathrm{Ir}$ insertion layer thickness because of the opposite spin Hall angle between $\mathrm{W}$ and $\mathrm{Ir}$, and the sign changes when the thickness of $\mathrm{Ir}$ is 1.5 nm, which is close to the spin diffusion length of $\mathrm{Ir}$ of 1.35 nm. Importantly, a 0.25-nm-thick $\mathrm{Ir}$ 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 $\mathrm{Ir}$ diffuses into ${\mathrm{Co}}_{20}{\mathrm{Fe}}_{60}{\mathrm{B}}_{20}$ and leads to the formation of ${\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Ir}}_{x}$. 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.