Current-Induced Magnetization Switching in Two Types of Nanopillar with Dual Fixed Layers

We study current-induced magnetization switching in nanofabricated magnetic multilayers with two different types of dual fixed layer structures. The first type is a single free layer with antiparallel aligned dual fixed layers. The second type is a synthetic antiferromagnetic (Syn.AF) free layer with parallel aligned dual fixed layers. In the former case, the switching current density (Jc) is reduced by a factor of more than two, as expected from our estimation. On the other hand, in the latter case, the dual structure does not reduce the Jc, which suggests the contributions of spin-dependent reflections and scatterings at various interfaces inside the free layer are significant. In some situations, they can reduce the total efficiency of the spin-transfer torque.