Real-Space Observation of Topological Defects in Extended Skyrmion-Strings

• Published in: Nano letters 2020-10, Vol.20 (10), p.7313-7320
• Main Authors: Yu, Xiuzhen, Masell, Jan, Yasin, Fehmi S, Karube, Kosuke, Kanazawa, Naoya, Nakajima, Kiyomi, Nagai, Takuro, Kimoto, Koji, Koshibae, Wataru, Taguchi, Yasujiro, Nagaosa, Naoto, Tokura, Yoshinori
• Format: Article
• Language: English
• ISSN: 1530-6984; 1530-6992
• DOI: 10.1021/acs.nanolett.0c02708

Exotic topological spin textures such as emergent magnetic monopole/anti-monopoles (hedgehog/anti-hedgehog) in the metastable extended skyrmion-strings attract much attention to the fundamental physics owing to their novel electromagnetic properties. However, the direct imaging of such spin textures is lacking. Here, we report the real-space observation of emergent magnetic monopoles involved in extended skyrmion-strings by Lorentz transmission electron microscopy (TEM) in combination with micromagnetic simulations. The in-plane extended skyrmion-strings are observed directly by Lorentz TEM to accompany the topological hedgehog-like defect, where the skyrmion-string terminates or merges with another skyrmion-string, as well as the surface-related defects where skyrmion-string bends 90° and ends on the surface. We also demonstrate the transformation of a metastabilized lattice of out-of-plane short skyrmion-strings into an in-plane array of extended skyrmion-strings by tuning the magnitude of oblique fields in a room-temperature helimagnet, revealing the stability of such topological spin textures and the possibility to control them.