  Effects of magnetic asymmetry on strongly coupled spin-vortex pairs with
parallel core polarization and antiparallel chirality in synthetic nanomagnets
are investigated. This includes vortex-core length asymmetry, biasing field
asymmetry, and pinning of one of the two vortex cores. Our experimental
observations as well as analytical and micromagnetic modeling show how magnetic
asymmetry can be used to differentiate magneto-resistively otherwise degenerate
multiple stable states of a vortex pair. These results expand the knowledge
base for spin vortex arrays in nanostructures and should be useful in light of
the recent proposals on coding information into multiple topological spin
states, such as single and multiple vortex core/chirality states.
