Interferometry: Three-Dimensional Visualization of Magnetic Skyrmions

Summary

Magnetic Skyrmions, with a topological charge of one, are inherent stability and are an ideal candidate for next-generation low-power electronics. We have developed a technique to reconstruct the bulk structure of a material using neutron small angle scattering. This work provides insight into the formation, stabilization, and transition pathways of a skyrmion lattice.

Description

Figure 1: Two-dimensional vector fields of  (a) a hedgehog  type magnetic skyrmion (b) a spiral type magnetic skyrmion. 

Credit: Taken from Wikimedia under its Creative Commons license

Magnetic Skyrmions are localized regions in a material where the atomic spins exhibit a defect swirling pattern (topological change equal to one). Skyrmions are unique because they behave like tiny, stable particles and require only ultralow current densities to manipulate. This makes them ideal candidates for next-generation low-power electronics, particularly in spintronics, a field exploring ways to use the spin of electrons rather than their charge.

However, studying skyrmions in three-dimensional materials has been a significant challenge. Most research has focused on two-dimensional (thin film) systems, where skyrmions appear as circular patterns (see Fig. 1). In three-dimensional materials, these patterns extend into "skyrmion tubes" (see Fig 2 a-d), which behave more like threads that can twist, merge, or even break apart.

We have developed a novel imaging method using neutron scattering data combined with a tomographic reconstruction technique. For the first study, our team examined a bulk material composed of cobalt, zinc, and manganese (Co₈Zn₈Mn₄), which is known to form skyrmions at room temperature. By applying an external magnetic field and carefully rotating the sample, we created a detailed 3D map of the skyrmion structures inside.

This research marks a significant step forward in the ability to image and understand skyrmions in real materials. The present work sheds light on the stabilization and evolution of a triangular skyrmion lattice through 3D topological transitions that exhibit a mixture of distinctive segmenting and branching (anti)monopole defects (Fig. 1e). Our neutron tomography techniques provide unique insights into skyrmion formation, annihilation and transition processes through (anti)monopole defects. We will continue studying micromagnetic materials over greater length scales and explore their dynamic processes.

Figure 2: Characteristic topological transitions present in the mean scattering feature reconstruction showing branching (B) and segmentation (S) (anti)monopole pathways. (a), segmentation monopole-antimonopole pair (b), combination of segmentation monopole and branching antimonopole (c), and a localized skyrmion filament structure cupped by a segmentation monopole-antimonopole pair (d). The blue contours outline the skyrmion tubes. Branching and segmentation emergent (anti)monopoles are observed to occur at transition points along the tubes, displaying distinct spin textures (e), Enlarged spin textures are shown for the labeled branching and segmentation (anti)monopoles with each spin corresponding to one voxel.

Credit: Figure and caption taken from Henderson et al., Nat. Phys. 19, 1617–1623 (2023)