Three-dimensional neutron far-field tomography of a bulk skyrmion lattice

Abstract

Magnetic skyrmions are localized non-collinear spin textures, characterized by an integer topological charge. Commonly observed in thin systems as two-dimensional sheets, in three dimensions skyrmions form tubes that are thought to nucleate and annihilate along their depth on points of vanishing magnetization. However, a lack of techniques that can probe the bulk of the material has made it difficult to perform experimental visualizations of skyrmion lattices and their stabilization through defects. Here we present three-dimensional visualizations of a bulk Co8Zn8Mn4 skyrmion lattice through a tomographic algorithm applied to multiprojection small-angle neutron scattering measurements. Reconstructions of the sample show a disordered skyrmion lattice exhibiting three-dimensional topological transitions through emergent (anti)monopole branching and segmentation defect pathways. Our technique provides insights into skyrmion stabilization and topological transition pathways in a bulk skyrmion lattice, guiding the future development and manipulation of skyrmion materials for spintronic applications.

Raman Shifts in Two-Dimensional van der Waals Magnets Reveal Magnetic Texture Evolution

“…It is noticeable that the shift value obtained based on this assumption is smaller than the experimental results, suggesting that the 3D magnetic textures of the skyrmions are very likely inhomogeneous within the penetration depth of the excitation light in Cr 2 Ge 2 Te 6 (∼90 nm) and deviate from straight cylindrical skyrmion tube shapes (see Supporting Information S5 for details). Indeed, recent depth-dependent studies revealed that substantial distortions and twisting in skyrmion spin textures often exist in magnetic thin films. − Our results indicate that such variations in the magnetic texture along the thickness direction could also exist in our Cr 2 Ge 2 Te 6 films.…”

“…44,45 spin−phonon coupling in Cr 2 Si 2 Te 6 , which we estimate to be 0.097 ± 0.040 cm −1 (Figure S7c). 28,38 Nevertheless, the Raman shifts observed in field-cooled Cr 2 Si 2 Te 6 thin films further confirm the intimate connection between the spin− phonon interaction and magnetic texture changes.…”

“…Above T c , a continuous blue-shift of the Raman modes can be observed with decreasing temperature (Figure 3e for the E g 3 mode and Figure S2b for A g 1 mode), which can be well described by an anharmonic model 28 (Figure 3e, red curve). At temperatures close to and below T c , the experimentally obtained Raman mode position apparently deviates from the anharmonic model and reaches a maximum value at 10 K. This deviation of the phonon mode position from the anharmonic model suggests the additional contribution from spin−phonon coupling at below T c : 28,38 the ⟨S i •S j ⟩ term in eq 1 changes from 0 for the paramagnetic phase at T > T c , to ∼9/4 for the ferromagnetic phase at 10 K in this zero-field-cooling process. From the latter, we can derive λ = 0.32 ± 0.057 cm −1 for the E g 3 mode, which agrees well with previous studies.…”

Skyrmion lattice formation and destruction mechanisms probed with TR-SANS

“…In a final consideration, these measurements were performed on bulk-materials, which are treated as homogeneous, linear skyrmion tubes 43 in the preceding discussions. However, recent works 44,45 have highlighted that the buried structure can be quite complex, including entanglement of tubes, non-topological skyrmion-like structures that terminate at either end, and branching between skyrmion tubes. Disentangling the tube may contribute significantly to the ordering timeframes.…”

“…Insul = insulator, >6 × 10 12 μΩ cm. All values were either measured or taken from ref [42][43][44][45][46].…”