Determination of spin Hall angle in heavy metal/CoFeB-based heterostructures with interfacial spin-orbit fields

TL;DR

This paper investigates spin Hall angles and interfacial spin-orbit fields in heavy metal/CoFeB heterostructures using SOT-FMR, revealing conditions for efficient magnetization switching through pure spin-current effects.

Contribution

It introduces an analytical model to determine spin Hall angles and interfacial spin-orbit fields, enhancing understanding of spin-current-induced magnetization dynamics in multilayers.

Findings

Spin Hall angle of -0.36 in W/CoFeB bilayers.

Spin Hall angle of 0.09 in CoFeB/Pt bilayers.

Interfacial spin-orbit fields can cancel Oersted fields, enabling pure spin-current dynamics.

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.