Spin-transfer in magnetic metallic nanopillars

Summary form only given. Presents experiments on spin-transfer induced magnetization reversal and excitations in magnetic metallic nanopillars. For these studies, sub-micron lateral dimension (∼50 nm) pillar devices have been fabricated by means of a new nano-stencil mask process ideal for systematic variation of layer composition and thickness. The author addresses three aspects of the physics of spin-transfer: (A) The phase-diagram for magnetic switching in bilayer (Co/Cu/Co) nanopillars in large magnetic fields applied perpendicular to the plane of the layers; (B) Current-induced excitations in single cobalt ferromagnetic layer (Cu/Co/Cu) nanopillars (i.e., in structures without a fixed spin-polarizing magnetic reference layer); and (C) the dependence of the switching current on free magnetic layer thicknesses in bilayer structures. In the latter case, the thickness of a cobalt layer has been systematically varied from 0.5 to 4 nm. However, the slope of the switching current, dI_c/dH, is found to have only a weak dependence on this thickness at low temperature (4.2 K), in contrast to the linear thickness dependence expected in the original model of spin-transfer. The author discusses interpretations of this behavior, including the possible importance of spin-pumping induced magnetic damping in these ultra-thin free magnetic layers.