A multi-level single-bit data storage device

One method to increase bit density in magnetic memory devices is to use larger structures that have multiple states in which to encode information rather than the typical two state system. A ferromagnetic nanoring with multiple domain walls that annihilate at different applied magnetic fields could serve as such a bit. This paper examines the formation and annihilation of four 360°domain walls (DWs) using micromagnetic simulations. To create the walls, one can apply circular magnetic fields to asymmetric nanoring structures. Nanorings with circular notches on a centered elliptical hole enable the formation of stable DWs in specific locations with known characteristics. By considering the impacts of both domain wall length and topological winding number on domain wall energy, one can create a nanostructure with four stable domain walls that annihilate at different applied magnetic fields. With two stable vortex configurations, such nanorings could theoretically encode up to ten different states. © 2014 AIP Publishing LLC.