Control and manipulation of a magnetic skyrmionium in nanostructures

TL;DR

This paper investigates the generation, manipulation, and transformation of magnetic skyrmioniums in nanostructures, revealing their dynamic behaviors and potential for skyrmion-based technologies.

Contribution

It provides a systematic study of skyrmionium dynamics, including their faster motion compared to skyrmions and the unzipping process into skyrmions under current influence.

Findings

Skyrmionium moves faster than skyrmions under out-of-plane current.

Skyrmionium and skyrmions have identical current-velocity relations with in-plane current.

Skyrmionium can be unzipped into two skyrmions via spin-polarized current.

Abstract

A magnetic skyrmionium is a nontopological soliton, which has a doughnut-like out-of-plane spin texture in thin films, and can be phenomenologically viewed as a coalition of two topological magnetic skyrmions with opposite topological numbers. Due to its zero topological number ($Q=0$) and doughnut-like structure, the skyrmionium has its distinctive characteristics as compared to the skyrmion with $Q=\pm 1$. Here we systematically study the generation, manipulation and motion of a skyrmionium in ultrathin magnetic nanostructures by applying a magnetic field or a spin-polarized current. It is found that the skyrmionium moves faster than the skyrmion when they are driven by the out-of-plane current, and their velocity difference is proportional to the driving force. However, the skyrmionium and skyrmion exhibit an identical current-velocity relation when they are driven by the in-plane current. It is also found that a moving skyrmionium is less deformed in the current-in-plane geometry compared with the skyrmionum in the current-perpendicular-to-plane geometry. Furthermore we demonstrate the transformation of a skyrmionium with $Q=0$ into two skyrmions with $Q=+1$ in a nanotrack driven by a spin-polarized current, which can be seen as the unzipping process of a skyrmionium. We illustrate the energy and spin structure variations during the skyrmionium unzipping process, where linear relations between the spin structure and energies are found. These results could have technological implications in the emerging field of skyrmionics.