Three-dimensional Neutron Far-Field Tomography of Skyrmions and Their Topological Defects

Magnetic skyrmions define a unique class of topological object, characterized by a multi-directional twisting of spins which nucleate and annihilate on magnetic singularities, called Bloch points. 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 the first experimental visualizations of three-dimensional skyrmion topological transition pathways across nucleation and annihilation phase trajectories in a bulk triangular lattice skyrmion host. Reconstructed spin textures uncover novel skyrmion formation pathways through field-perpendicular tubes, while stabilized tubes exhibit a zoology of exotic three-dimensional metastable topological structures and bundles. We explore skyrmion phase energetics and topological stability through tunable magnetic field sequences, highlighting skyrmion dynamics through a coupling of merons and monopoles. Our results provide unprecedented access to three-dimensional topological phenomena which overturn previous architectures of skyrmion nucleation and manipulation, reimagining spintronic frameworks through new control pathways and encoding structures.