  The switching of a vortex core of a single disk in an array of a multilayer
system is investigated by micromagnetic simulation. We found that the
perpendicular uniaxial anisotropy (PUA) decreases the frequencies of the
azimuthal mode in disks with magnetic vortex configuration. We obtained a phase
diagram of magnetic field intensity vs. frequency of the azimuthal mode, as a
function of the value of perpendicular uniaxial anisotropy. We demonstrated
that rotating magnetic fields (CW and CCW) with frequency equal to azimuthal
modes can be used to switch the vortex core of single disks in a disk array.
This allows obtaining different memory states with a single array of nanodisks,
and therefore writing information through the application of rotating fields.
