Determination of Spin Hall Angle in Heavy-Metal/Co−Fe−B-Based Heterostructures with Interfacial Spin-Orbit Fields

The magnetization dynamics in W/Co20Fe60B20, Co20Fe60B20/Pt and W/Co20Fe60B20/Pt multilayers are investigated using spin-orbit-torque ferromagnetic resonance (SOT FMR) technique. An analytical model based on magnetization dynamics due to SOT is used to fit the heavy-metal (HM) thickness dependence of the symmetric and antisymmetric components of the SOT FMR signal. The analysis results in a determination of the properties of the HM layers, such as the spin Hall angle and the spin diffusion length. Spin Hall angles of -0.36 and 0.09 are found in the W/Co20Fe60B20 and Co20Fe60B20/Pt bilayers, respectively, which add up in the case of a W/Co20Fe60B20/Pt trilayer. More importantly, we determine the effective interfacial spin-orbit fields at both the W/Co20Fe60B20 and Co20Fe60B20/Pt interfaces, which are shown to cancel the Oersted field for particular thicknesses of the heavy-metal layers, leading to pure spin-current-induced dynamics and indicating the possibility of more efficient magnetization switching.