Direct observation of spin configurations and classification of switching processes in mesoscopic ferromagnetic rings

Using nonintrusive imaging techniques we have directly observed the nanoscopic details of the magnetization configurations of epitaxial and polycrystalline mesoscopic ring structures with a <15-nm resolution. We have found head to head domain walls with different spin structures depending on ring width. Further, we can classify the geometry dependent switching processes according to the number of transitions (single, double, triple) that a ring undergoes in a hysteresis cycle. In the case of triple switching we find a state with a complete vortex core present in the ring.