Large vortex state in ferromagnetic disks

Abstract: Magnetic vortices in soft ferromagnetic nano-disks have been extensively studied for at least several decades both for their fundamental (as a "live" macroscopic realization of a field theory model of an elementary particle) as well as applied value for high-speed high-density power-independent information storage. Here it is shown that there is another stable vortex state with large thickness-dependent core profile in nano-scale ferromagnetic disks of several exchange lengths in size. Its energy is computed numerically (in the framework of Magnetism@home distributed computing project) and its stability is studied analytically, which allows to plot it on magnetic phase diagram. In cylinders of certain geometries large vortices exist on par with classical ones, while being separated by an energy barrier, controllable by tuning the geometry and material of ferromagnetic disk. They can be an excellent candidate for magnetic information storage not only because the resulting disk sizes are among the smallest, able to support magnetic vortices, but also because it is the closest to the classical vortex state of all other known metastable states of magnetic nano-cylinder. It means that memory, based on switching between these two types of magnetic vortices, may, potentially, achieve the highest possible rate of switching.