Magnetic imaging of various topological spin textures and their dynamics

[摘要] Nanometer-scale vortex-like topological spin textures, such as magnetic skyrmion and antiskyrmion, have recently attracted enormous attention owing to their topological nature and emergent electromagnetic properties. To confirm such minute twisted spin textures and their dynamics under external stimuli, real-space imaging techniques with high spatial resolution and high recording speed are required. To realize the Bloch-type magnetic skyrmion with a topological number of - 1 (where spins swirl from the north-pole in the core to the south-pole in the peripheral, and wrap a sphere), we have developed a technique allowing not only to create skyrmions via precise control of the magnetic field in a standard transmission electron microscope (TEM), but also to directly demonstrate their twisted textures and dynamics. We employed a phase imaging technique, called differential-phase contrast, in the scanning TEM mode to quantitatively characterize Neel-type magnetic twists, such as Bloch lines, that constitute the antiskyrmion with a topological number + 1. Furthermore, we took advantage of cryogenic high-resolution Lorentz TEM to probe atomic-scale skyrmions in a centrosymmetric magnet with a Ruderman-Kittel-Kasuya-Yosida coupling. To manipulate and track individual skyrmions and their lattice using a relatively low electric current, combined with field-quenching of skyrmions, we designed a thin FeGe microdevice having a notch, in which the spin current was localized in the specific area near a corner of the notch. Using this device, we tracked drift, Hall, and torque motions of single 80-nm-sized skyrmions and their bunches using electric current densities three orders of magnitude lower than those required to manipulate magnetic domain walls.

[发布日期] 2021-12-01