Rich topological spin textures in single-phase and core-shell magnetic nanodisks

Magnetic skyrmions have potential applications in future high-density information storage devices due to their small size, topologically protected structure, and ultralow energy consumption. Here, we use a variational method to study rich topological spin textures in magnetic nanodisks, including skyrmions and skyrmionlike objects. The existence of skyrmions and k pi-skyrmions in a single-phase nanodisk and a disk with a core-shell structure is investigated theoretically, where the phase diagrams of possible spin states are obtained for various Dzyaloshinskii-Moriya interaction (DMI) constants and disk dimeters. Our calculations suggest that skyrmions can be generated spontaneously in a core-shell nanodisk. We also study the transitions of spin textures in the nanodisk induced by spin currents. This paper may provide guidelines for experimental realization of different topological spin textures in nanodisks with certain DMIs. The simple two-dimensional analytical method used in this paper can be used to study the magnetic phase diagrams of thin films with interface-induced DMIs.