Field evolution of magnetic vortex state in ferromagnetic disks

The evolution of a magnetic vortex state in submicron ferromagnetic disks has been studied as functions of disk diameter and thickness. The vortex core displacement in the applied magnetic field was calculated by minimizing the total magnetic energy consisting of the magnetostatic, exchange, and Zeeman energies. A simple analytical expression fur the initial magnetic susceptibility is deduced. The initial susceptibility increases with increasing disk diameter and decreasing thickness. The calculations agree well with the experimental data obtained fur the 60 nm thick permalloy disk arrays with a variable diameter from 0.2 to 0.8 mum. (C) 2001 American Institute of Physics.