Effects of capping layer on the spin accumulation and spin torque in magnetic multilayers

Abstract

We study the effects of the physical properties of the capping layer (spin diffusion length (SDL), resistivity and interface resistance) on the spin transfer torque (STT) and spin accumulation in the free ferromagnetic (FM) layer of a magnetic multilayer system. The STT and spin accumulation are calculated based on a non-collinear spin drift–diffusion (SDD) model under the assumption of quasi-interfacial absorption of transverse spin accumulation in the FM layers. It is found that the out-of-plane component of the STT in the free FM layer is significantly enhanced by having a thick, highly resistive capping layer, with a long SDL. The in-plane torque component is, however, insensitive to variations in the capping layer properties. The implications of these trends to applications, such as current-induced magnetization switching and spin torque oscillations, are discussed.