Magnetization reversal in Pac-Man shaped Fe nanostructures with varying aperture

Round magnetic nano-dots belong to the frequently investigated magnetic nanostructures since they can often reverse magnetization via a vortex state which is characterized by low stray fields, making them useful for data storage applications. Nano-rings, with an open aperture in the middle, regularly show flux-closed vortex states without a vortex core, again reducing stray fields. Here we theoretically investigate “Pac-Man” shaped iron nanostructures with varying aperture, i.e. structures ranging from a thin ring to a solid cylinder with a triangular cut. Our results show that in most cases, a vortex-like state without vortex core along the whole nanostructure occurs during magnetization reversal. Depending on the angle of the external magnetic field and the nanostructure thickness, different magnetization reversal processes have been found, including domain wall nucleation and propagation as well as small vortex states with cores. The occurrence of such special magnetic states can be attributed to the interaction of the shape anisotropy with the relatively high magneto-crystalline anisotropy of iron. Our simulations reveal the possibilities to use such structures for data storage applications as well as their importance in basic research, enabling formation of asymmetric magnetic structures beyond common onion and symmetric vortex states.