Using transmission electron microscopy and quantitative electron holography magnetic imaging techniques, a collaborated research team led by Prof. DU Haifeng from Hefei Institutes of Physical Science, Chinese Academy of Sciences discovered a topological phase transition from magnetic solitons to skyrmions in a monoaxial chiral magnet, Cr1/3NbS2 recently.
The research results, which were published in Advanced Materials, represent an important advance in the investigation of topological magnetic structures. They were fundamental to the development of new magnetic storage devices, according to the team.
In chiral magnets, the formation of topological magnetic structures and spin configurations depends on the type of Dzyaloshinskii-Moriya (DM) interaction. Topological magnetic structures with different spin configurations can transform. Using two different types of topological magnetic structures to store binary data "0" and "1" in a single material has practical significance for building topological magnetic storage devices. However, the topological transformation between chiral magnetic solitons and skyrmions has been limited due to the different types of DM interaction.
To address this issue, the team used the geometric boundary domain effect to modulate the magnetic structure at both ends of the magnetic solitons, breaking the limitations of the DM interaction and achieving a topological phase transition from magnetic solitons to skyrmions in Cr1/3NbS2.
They discovered that the newly formed skyrmions were adjustable in length, and their upper and lower ends were composed of two topological charges of 1/2, with a total topological charge of 1 unit for the topological magnetic structure. Experimental results also showed the thickness dependence of this topological phase transition, indicating the important role of dipole-dipole interactions in the transition process, consistent with the results of micromagnetic simulations.
"Our discovery enriched the topological magnetic structure family and had significant implications for building new magnetic-electronic devices," said LI Long, the first author of the paper.
Types of DM interactions and corresponding topological magnetic structures (left)
Magnetic skyrmion found in the uniaxial chiral magnet Cr1/3NbS2 revealed by electron holography technique (right)(Image by LI Long)
