  We experimentally study the structure and dynamics of magnetic domains in
synthetic antiferromagnets based on Co/Ru/Co films. Dramatic effects arise from
the interaction among the topological defects comprising the dual domain walls
in these structures. Under applied magnetic fields, the dual domain walls
propagate following the dynamics of bi-meronic (bi-vortex/bi-antivortex)
topological defects built in the walls. Application of an external field
triggers a rich dynamical response: The propagation depends on mutual
orientation and chirality of bi-vortices and bi-antivortices in the domain
walls. For certain configurations, we observe sudden jumps of composite domain
walls in increasing field, which are associated with the decay of composite
skyrmions. These features allow for enhanced control of domain-wall motion in
synthetic antiferromagnets with the potential of employing them as information
carriers in future logic and storage devices.
