Magnetic Skyrmion Bundles and Their Current-Driven Dynamics

Abstract: Quantization of topological charges determines the various topological spin textures that are expected to play a key role in future spintronic devices. While the magnetic skyrmion with a unit topological charge Q has been extensively studied, spin textures with other integer valued have not been verified well so far. Here, we report the real-space image, creation, and manipulation of a type of multi Q three-dimensional skyrmionic texture, where a circular spin spiral ties a bunch of skyrmion tubes. We define these objects as skyrmion bundles, and show they have arbitrarily integer values Q from negative up to at least 55 in our experiment. These textures behave as quasiparticles in dynamics for the collective motions driven by electric pulses. Similar to the skyrmion, skyrmion bundles with non zero Q exhibit the skyrmion Hall effects with a Hall angle of 62 degree. Of particular interest, the skyrmion bundle with Q = 0 propagates collinearly with respect to the current flow without the skyrmion Hall effect. Our results open a new perspective for possible applications of multi Q magnetic objects in future spintronic devices.