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 c ore displacement in the applied magnetic field was calculated by minimizing the total magnetic energy consisting of the magnetostatic, exchange, and Z eeman energies. A simple analytical expression fur the initial magnetic sus ceptibility is deduced. The initial susceptibility increases with increasin g disk diameter and decreasing thickness. The calculations agree well with the experimental data obtained fur the 60 nm thick permalloy disk arrays wi th a variable diameter from 0.2 to 0.8 mum. (C) 2001 American Institute of Physics.