Interface effect of ultrathin W layer on spin-orbit torque in Ta/W/CoFeB multilayers

Abstract

The effect of an ultrathin W interlayer on the perpendicular magnetic anisotropy (PMA), spin orbit torque (SOT), and SOT-induced magnetization switching of Ta/CoFeB/MgO films has been investigated. Both the anisotropy energy density and the spin-torque efficiency are enhanced by inserting the ultrathin W interlayer. The results suggest that the large enhancement of the spin-torque efficiency originates from the increase in the interfacial spin transparency using a simplified drift-diffusion model. The minimum in-plane field required for SOT-induced complete switching is reduced to 12 Oe for the sample with the W interlayer, which is confirmed by polar Kerr microscopy. The reversed domain nucleation and propagation of the reversal processes have been observed by Kerr imaging. It is concluded that the ultrathin W interlayer increases the spin transmission and reduces the strength of the Dzyaloshinskii–Moriya interaction. Our result suggests that the interface modification is an efficient way to modulate the PMA and SOT.