Current-Induced Dynamics in Almost Symmetric Magnetic Nanopillars
  Magnetic nanodevices usually include a free layer whose configuration can be changed by spin-polarized current via the spin transfer effect, and a fixed reference layer. Here, we demonstrate that the roles of the free and the reference layers interchange over a small range of their relative thicknesses. Precession of both layers can be induced by spin transfer in symmetric devices, but the dynamics of one of the layers is rapidly suppressed in asymmetric devices. We interpret our results in terms of the dynamical coupling between magnetic layers due to spin transfer. 
Weng Lee Lim, Andrew Higgins, Sergei Urazhdin