Confinement of stable skyrmionium and skyrmion state in ultrathin nanoring

Abstract

Magnetic skyrmionium is a donut-shaped spin texture with zero topological number (Q) and has promising application in future spintronic devices. In this work, using micromagnetic simulation based on Landau-Lifshitz-Gilbert (LLG) equation, we report the generation of skyrmionium in an ultrathin magnetic nanoring in the presence of Dzyaloshinskii-Moriya interaction (DMI) and external magnetic field. By varying the DMI strength and outer diameter of a nanoring, the possibilities of creation of other skyrmion states (kπ states) are explored and we have reported the existence of 3π state and 4π state in nanoring for the first time. Also, we report that the transition of skyrmion state from kπ to (k-1)π occurs for a few millitesla (mT) magnetic fields in the out-of-plane configuration. Further, we have demonstrated the degeneration of skyrmionium (Q=0) into an isolated skyrmion (Q=±1) and a pair of skyrmions (Q=−2) in a nanoring of small dimension by applying an in-plane spin-polarized current. A complete study of the generation of skyrmionium and its topological stability is done by performing the micromagnetic simulation. Our results will provide guidelines for the design of spin-polarized current-controlled skyrmionium-skyrmion based spintronic memory and logic devices.