Research progress in the magnetic domain wall topology

Abstract

Topological magnetic skyrmions, as information units, possess distinct advantages such as high reliability, enhanced integration, and low energy consumption. These novel topological characteristics offer critical material and technological support for the rapid development of information technology, 5G communication, and big data. However, the application of magnetic skyrmions in practical devices is severely impeded by certain limitations, including their stability dependence on magnetic field and the deflection caused by the skyrmion Hall effect under electric current. Consequently, exploring new topological magnetic domain structures and material systems suitable for application becomes a pivotal area of research. This paper primarily focuses on experimental studies utilizing high-resolution Lorentz transmission electron microscopy for <i>in situ</i> real-space observation and manipulation of topological merons and skyrmions inside the magnetic domain wall, confirming the theoretical prediction of magnetic domain wall skyrmions in 2013. We has firstly achieved topological meron chains inside the domain walls by using the spin reorientation transition in two-dimensional van der Waals Fe_5–<i>x</i>GeTe₂ magnets, and systematically studied the dynamic behavior of domain wall topological magnetic domain structures under external electric and magnetic fields, filling the blanks in this research area. The important and special roles of magnetic domain walls are revealed at the same time. Then the GdFeCo amorphous ferrimagnetic thin film was designed and prepared based on the summarized mechanism with the domain wall meron pairs successfully reproduced. Moreover, the reversible topological transformation from domain wall meron pair to domain wall skyrmions has also been realized without external magnetic field during spin reorientation transformation as temperature changing. The results of micromagnetic simulation and electric experiments on the topological domains in domain walls would provided a strong basis and support for the future research.