Unwinding Skyrmions in Three Dimensions Through Vortices and Monopoles

Magnetic skyrmions represent non-collinear topological spin textures which nucleate and annihilate on magnetic singularities. In three dimensions, their stabilization into flexible tubes introduces enhanced dimensionalities and emergent phenomena which endows them with superior functionalities as information carriers in future spintronic devices. Unfortunately, a lack of bulk probes has prevented their complete characterization in three dimensions, inhibiting the development of modern skyrmion device architectures. Here, we present novel experimental visualizations of three-dimensional skyrmion field-induced topological transition pathways across various bulk triangular lattice skyrmion hosts with tunable disorder. Ordered skyrmion states reveal exotic periodic modulations, while disordered states uncover a zoology of exotic metastable Q=0 skyrmion bundles with novel transition pathways via the coupling of merons and monopoles. We explore skyrmion phase energetics as a function of compositional disorder, highlighting topological transitions through vortex and defect-mediated pathways. Our results provide unrivaled access to three-dimensional skyrmion phenomena across diverse compositional systems, unveiling novel methods of nucleation and control to reshape future devices.