  Within the Ginzburg-Landau formalism, we predict two novel mechanisms of
vortex-antivortex nucleation in a magnetically nanostructured superconductor.
Although counterintuitive, nucleation of vortex-antivortex pairs can be
activated in a superconducting (SC) film covered by arrays of submicron
ferromagnets (FMs) when exposed to an external homogeneous magnetic field. In
another scenario, we predict the thermal induction of vortex-antivortex
configurations in SC/FM samples. This phenomenon leads to a new type of
Little-Parks oscillations of the FM magnetization-temperature phase boundary of
the superconducting film.
