Vortex-antivortex pair driven magnetization dynamics studied by micromagnetic simulations

Magnetization dynamics approaching an equilibrium vortex state from an initial nonequilibrium state under zero magnetic field has been studied in a circular-shaped Fe disk with a thickness of 5 nm and a diameter of 1200 nm using micromagnetic simulations. Upon starting from the initial random configuration of in-plane magnetizations, a great number of vortex (V)-antivortex ((V) over bar) pairs are generated at a lot of nucleation sites where both types of V and (V) over bar are energetically favorable to form. The V and (V) over bar are propagated and then annihilated by their attractive interactions during the relaxation dynamic process. These results reveal that temporal magnetization evolutions can be dominated by the nucleation of V-(V) over bar pairs, followed by their propagation and annihilation. The dynamic process driven by V-(V) over bar pairs can play a significant role in various magnetization reversals. (C) 2004 American Institute of Physics.