Nucleation and dynamic switching of magnetic vortices in geometrically confined nanodots

Magnetic vortices are characterized by the sense of in-plane magnetization circulation and by the polarity of the vortex core. Due to the combination of controlled chirality and polarity, magnetic vortices have attracted scientific interest for their potential application as multibit memory cells. However, to obtain the stable ground state, the confined geometries of the vortex structures define a threshold value as a result of competition between magnetostatic and exchange energies. In this article a novel cylinder-groove (CG) model is presented to favor vortex formation in magnetic nanodots of small critical dimension, which is confirmed by micromagnetic simulations. Micromagnetic simulation was carried out to study initial state and dynamical behavior of modified Permalloy nanodot using the Object Oriented Micromagnetic Framework (oommf) code based on the Landau-Lifshitz-Gilbert equation. For the Permalloy material parameters, we used the saturation magnetization M_s=8 .6×105 A/m, the exchange stiffness A_ex=1 .3×10-11 J/m, and negligible magnetocrystalline anisotropy. The nanodots were discretized into cubed with dimensions of 4×4×4 nm, which is smaller in length scale than the exchange length. The stable vortex is excited by externally in-plane magnetic field bursts.