  Magnetic vortices have generated intense interest in recent years due to
their unique reversal mechanisms, fascinating topological properties, and
exciting potential applications. Additionally, the exchange coupling of
magnetic vortices to antiferromagnets has also been shown to lead to a range of
novel phenomena and functionalities. Here we report a new magnetization
reversal mode of magnetic vortices in exchange coupled Ir20Mn80/Fe20Ni80
microdots: distorted viscous vortex reversal. Contrary to the previously known
or proposed reversal modes, the vortex is distorted close to the interface and
viscously dragged due to the uncompensated spins of a thin antiferromagnet,
which leads to unexpected asymmetries in the annihilation and nucleation
fields. These results provide a deeper understanding of the physics of exchange
coupled vortices and may also have important implications for applications
involving exchange coupled nanostructures.
