Micromagnetic Study of Spin Transfer driven Vortex Dipole and Vortex   Quadrupole Dynamics
  Vortices and antivortices are typical non uniform magnetization configurations that can be achieved in spin-torque oscillators with in-plane materials. Dynamics of a vortex-antivortex pair, namely vortex dipole, were predicted and already observed. In this paper, we present a systematic micromagnetic study on that kind of dynamics in different spin-valves where the current is injected through a nano-aperture. Rotation and translation of vortex dipoles and rotation of vortex quadrupoles are shown depending on the shape and the size of the spin-valve. The origin of the different behaviors is explained within a micromagnetic framework. 
A. Giordano, V. Puliafito, L. Torres, M. Carpentieri, B. Azzerboni,   and G. Finocchio
nlin.PS