  A magnetic nanoparticle in a vortex state is a promising candidate for the
information storage. One bit of information corresponds to the upward or
downward magnetization of the vortex core (vortex polarity). Generic properties
of the vortex polarity switching are insensitive of the way how the vortex
dynamics was excited: by an AC magnetic field, or by an electrical current. We
study theoretically the switching process and describe in detail its mechanism,
which involves the creation and annihilation of an intermediate
vortex-antivortex pair.
