Broadband probing magnetization dynamics of the coupled vortex state   permalloy layers in nanopillars
  Broadband magnetization response of coupled vortex state magnetic dots in layered nanopillars was explored as a function of in-plane magnetic field and interlayer separation. For dipolarly coupled circular Py(25 nm)/Cu(20 nm)/Py(25 nm) nanopillars of 600 nm diameter, a small in-plane field splits the eigenfrequencies of azimuthal spin wave modes inducing an abrupt transition between in-phase and out-of-phase kinds of the low-lying coupled spin wave modes. The critical field for this splitting is determined by antiparallel chiralities of the vortices in the layers. Qualitatively similar (although more gradual) changes occur also in the exchange coupled Py(25 nm)/Cu(1 nm)/Py(25 nm) tri-layer nanopillars. These findings are in qualitative agreement with micromagnetic dynamic simulations. 
Ahmad A. Awad, Antonio Lara, Vitali Metlushko, Konstantin Y.   Guslienko, and Farkhad G. Aliev
cond-mat.mes-hall cond-mat.mtrl-sci cond-mat.other physics.comp-ph