Frequency domain studies of current-induced magnetization dynamics in   single magnetic-layer nanopillars
  Spin transfer torque-induced high-frequency dynamics of single thin cobalt-layer nanopillars of circular and elliptical shape have been observed directly. Two types of precessional modes can be identified as a function of magnetic field perpendicular to the layer plane, excited for negative current polarity only. They are assigned to vortex-core and transverse spin-wave excitations, which corroborate recent model predictions. The observed narrow linewidth of 4 MHz at room temperature indicates the high coherence of the magnetic excitations. 
N. M\"usgens, S. Fahrendorf, T. Maassen, A. Heiss, J. Mayer, B.   \"Ozyilmaz, B. Beschoten, and G. G\"untherodt
cond-mat.mtrl-sci cond-mat.mes-hall