Spin configurations and classification of switching processes in ferromagnetic rings down to sub-100 nm dimensions

The magnetic states and switching processes are investigated in Co and NiFe rings with lateral dimensions from the micrometer range down to sub-100 nm. Using non-intrusive imaging techniques we have directly observed the nanoscopic details of the magnetization configurations of epitaxial and polycrystalline mesoscopic ring structures with < 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 novel state with a complete vortex core present in the ring. It is found that the double switching can be retained in sub-100 nm rings by tailoring the material and thickness.