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

Abstract

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

Field-Free Spin-Orbit-Torque Switching in Co / Pt / Co Multilayer with Mixed Magnetic Anisotropies

“…As a result, the spin Hall angle of θ = 0.08 is obtained, which agrees with literature values for this material. 26,27 Note, that in Fig. 3(d) the effective spin Hall angle, θ eff ≈ 0.1, obtained roughly from ratio V S /V A is slightly larger than the spin Hall angle of Pt, θ = 0.08, obtained from fitting the model derived in Ref.…”

“…which is determined by thickness-independent spin-orbit coupling strength Γ SO . 26 We consider here this contribution as originating from interfacial spin-orbit coupling, and distinct from spin Hall contribution, as predicted theoretically, 30 although it is still the subject of ongoing debate. Experimental works, however, seem to confirm the possible Rashba-Edelstein origin of the field.…”

“…Spin transport properties of Pt, such as spin Hall angle and spin diffusion length, were determined using a dedicated model based on Ref. [26]. Mixing voltage, V mix , was obtained from the SOT-FMR measurement as a function of magnetic field, H, and the results are presented in Fig.…”

Current‐Induced Magnetization Switching by the High Spin Hall Conductivity α‐W

“…This allows the deposition of α‐W films in the thin regime. Also note that our deposition rate of W is controlled at ≈0.02 nm s −1 , which has been shown to favor the formation of β‐W in the normal structure . However, the same deposition condition results in α‐W for the reversed case.…”

“…The transmitted spin angular momentum can then be transferred to the local magnetic moments in the FM layer and generate spin–orbit torque (SOT)‐driven dynamics such as magnetization switching, magnetic oscillation, or domain wall (DW) motion . It has been previously shown that among pure 5d HMs, amorphous‐W (or also β‐W) has the largest damping‐like (DL) SOT efficiency or spin Hall ratio of ≈0.20–0.50 . However, when compared with other large SOT efficiency materials such as Pt‐based alloys or conductive topological insulators, amorphous‐W is less favorable for applications due to its high resistivity ( ≈ 200–300 μΩ cm) and, therefore, greater power consumption to achieve current‐induced SOT‐driven magnetization switching.…”