  Vortex pairs in magnetic nanopillars with strongly coupled cores and pinning
of one of the cores by a morphological defect, are used to perform resonant
pinning spectroscopy, in which a microwave excitation applied to the nanopillar
produces pinning or depinning of the cores only when the excitation is in
resonance with the rotational or gyrational eigenmodes of the specific initial
state of the core-core pair. The shift in the eigenmode frequencies between the
pinned and depinned states is determined experimentally and explained
theoretically, and illustrates the potential for multi-core spin-vortex memory
with resonant writing of information on to various stable vortex pair states.
Further, it is shown how the same resonant spectroscopy techniques applied to a
vortex pair can be used as a sensitive nanoscale probe for characterizing
morphological defects in magnetic films.
