Mechanism of Fast Axially--Symmetric Reversal of Magnetic Vortex Core
  The magnetic vortex core in a nanodot can be switched by an alternating transversal magnetic field. We propose a simple collective coordinate model which describes comprehensive vortex core dynamics, including resonant behavior, weakly nonlinear regimes, and reversal dynamics. A chaotic dynamics of the vortex polarity is predicted. All analytical results were confirmed by micromagnetic simulations. 
Oleksandr V. Pylypovskyi and Denis D. Sheka and Volodymyr P. Kravchuk   and Yuri Gaididei and Franz G. Mertens
cond-mat.mes-hall cond-mat.str-el