Direct Demonstration of Topological Stability of Magnetic SkyrmionsviaTopology Manipulation

The topological concept, initially introduced in particle physics, brought new excitements to many other fields of physics, such as topological insulators, ultracold atoms, and topological lasers to unveil various robust states therein. In nanomagnetism, the most prominent example governed by topology is the magnetic skyrmion. Since magnetic skyrmions exhibit a nontrivial topological property, it is expected that skyrmions are robust against external perturbations. Therefore, it has sparked considerable interest due to the academic interest and the prospect of employing the skyrmions as the nanometer-scale non-volatile information carriers. Although profound the concept is, the realistic situation that magnetic moments are localized in a discrete atomic lattice raises an immediate question of whether the topological concept is still viable in the real system. Despite the fundamental importance, the thorough assessment has remained elusive due to the challenge of controlling topology and thereby directly comparing the topologically nontrivial skyrmions and trivial bubbles in a single specimen.

In this work, we first show how to manipulate magnetic topology. By tuning a magnetic field pathway, we could selectively prepare either a skyrmion state or bubble state in the same material. Based on this method, we then show how robust the magnetic skyrmion structure is compared to the stability of topologically trivial bubbles. By measuring the lifetimes of both skyrmions and bubbles in the same specimen under the same magnetic fields, we found that magnetic skyrmions exhibit far longer lifetimes with much smaller sizes, directly evidencing the topological effect in a real discrete system. Our results corroborate the physical importance of the topology in the magnetic materials and open up a versatile route towards topology manipulation, which will facilitate the implementation of ever-stable nanometer-scale magnetic devices.