Three-Dimensional Neutron Far-Field Tomography of a Bulk Skyrmion Lattice

TL;DR

This paper introduces a novel tomographic neutron scattering method to visualize and analyze three-dimensional bulk skyrmion lattices and their topological defects, advancing understanding of their structure and stability.

Contribution

The study develops a new 3D neutron tomography algorithm for visualizing bulk skyrmion lattices and their defects, enabling detailed topological analysis in three dimensions.

Findings

Reconstructed disordered skyrmion lattice with 63% topological saturation

Identified two types of emergent monopole defect pathways with specific densities

Validated the method with digital phantoms and applied it to experimental data

Abstract

Skyrmions are topologically-protected spin textures thought to nucleate and annihilate on points of vanishing magnetization, called Bloch points. However, owing to a lack of bulk techniques, experimental visualizations of skyrmion lattices and their stabilization through defects in three-dimensions remain elusive. Here, we present a tomographic algorithm applied to a Co$_8$Zn$_8$Mn$_4$ skyrmion lattice host, processing multi-projection small angle neutron scattering measurements to generate mean scattering feature reconstructions (MSFR) of the bulk spin textures. Digital phantoms validated the algorithm; reconstructions of the sample show a disordered skyrmion lattice with a topological saturation of 63~\%, exhibiting three-dimensional topological transitions through two different emergent (anti)monopole defect pathways with densities of 147~$\mu$m$^{-3}$ and 21~$\mu \mathrm{m}^{-3}$ for branching and segmentation events, respectively. Our techniques produce experimentally-informed visualizations of bulk skyrmion lattice structures and defects, enabling future bulk studies over a wide variety of sample shapes and chemistries, magnetic phases, and external parameters.