Three-dimensional Visualization of Skyrmion Lattice Texture with Soft X-ray Vector Ptycho-Tomography.

Nanoscale topological defects in spin texture called magnetic skyrmions have recently attracted great interest for next-generation energy-efficient data storage and computing due to their topological protection with associated high energy barriers for decay. While skyrmions are traditionally stabilized through Dzyaloshinsky-Moriya interactions (DMI), skyrmion hexagonal lattices can also be stabilized by interlayer dipolar interaction in Fe/Gd multilayer thin films at room temperatures and zero external magnetic fields. However, direct visualization of 3D spin textures is very challenging, due to their small exchange length scale down to only a few nanometers and weak signal contrast of purely magnetic structures compared to nanoscale structural (i.e. charge) orders. Moreover, the need to scan over an extended region adds additional hurdles to imaging such systems. Here we represent a 3D visualization procedure based on soft X-ray vector ptycho-tomography that can successfully image 3D skyrmion lattice structures with unprecedented spatial resolution and field of view. Critical to validating our approach is the use of fiducial markers, as well as detailed comparison with computational imaging theory. Our results confirm micromagnetic simulations, which suggests the formation of hybrid skyrmion tubes with rotating helicities along the thickness of multilayer. This procedure enables researchers to observe directly how these nanoscale hybrid lattices are structured in full 3D, which is extremely valuable for their future spintronic applications.