  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.
