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 ( J c ) 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 J c , 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.