Topologically protected magnetic structures in perforated multilayer films.

The paper theoretically studies thin ferromagnetic films obtained by successive deposition of layers of easy-axis and easy-plane materials. It is shown that in films of this type, under certain conditions, effective anisotropy can arise, leading to the appearance of new directions of easy magnetization, set of which is divided into two independent orbits. The structure of domain walls (DWs) arising as a result of the transition of the magnetization vector from one orbit to another was studied. It has been proven that in the presence of perforations in the films under consideration, topologically protected inhomogeneities can arise, which are localized in the vicinity of two closely spaced holes and can be in one of six nonequivalent states, as a result of which paired perforations can be considered as memory cells for recording data in a base 6 number system. A numerical experiment has demonstrated that two adjacent cells can actually independently encode two digits in the specified number system due to the possibility of forming thin DWs between the cells.