3D rendering at Skyrmion – Micro X-ray fluoroscopy reveals 3D spin structure of tiny magnetic vortices

New insights: Physicists have mapped the fine 3D structure of skyrmions — tiny magnetic vortices in solid materials that are a promising basis for future “spin electronics.” Microscopic X-ray fluoroscopy has revealed for the first time how individual atomic spins in skyrmions are aligned and how they change with the height and width of magnetic vortices. This paves the way for the production of tailor-made skyrmions – for example for quantum memories and quantum computers in the future.

Whether skyrmions, hopfions, or other quantum structures: Strange spin structures can be created in some materials – magnetic microscopic structures created by a special alignment of atomic spins. Such topological magnetic structures can be very stable and behave like quasiparticles. Skyrmions in particular — tiny tornadoes made of twisted coils against each other — are promising candidates for data storage, quantum computers, and other quantum applications.

The 3D structure is not yet known

The two-dimensional structure of skyrmions has already been well studied: “Magnetic skyrmions are particle-like topological solitons whose magnetism at the center points in the opposite direction to that in the outer region,” explains David Raftery of Lawrence Berkeley National Laboratory. And his colleagues. But how the spins change with height, and thus the third dimension of the skyrmion, is only partially known so far.

However, it is precisely this knowledge that is necessary to make Skyrmions practically usable: in the world of electronics and silicon chips, Skyrmions must be treated as 3D objects, physicists explain. You must be able to accurately understand how the energy and direction of the rotations change within one of these small tornadoes – this is the only way to tailor it to the desired purposes.

Multilayer test disk in X-ray light

To illustrate this, Raftery and his team have now used a new form of X-ray analysis, called magnetic X-ray lamography. For the X-rays, they used a disk just 95 nanometers thick, made of several layers of iridium, cobalt and platinum as a test object. “These multilayer magnetic materials are known to exhibit textural responses that are sensitive to changes in the arrangement and thickness of the layers,” the physicists explain. “This allows the creation of topological structures such as skyrmions and hopfions.”

The team then exposed the skyrmions created in this material to a micro-X-ray beam from the Swiss Light Source at the Paul Scherrer Institute in Switzerland. The disk and its celestial structures are illuminated at different angles by soft X-rays. Similar to computer tomography, counting individual images yields a comprehensive picture of the 3D structure – in this case the 3D magnetic microstructure of the sample.

“The structure of Skyrmion can then be reconstructed from these countless images and data,” Raftery explains. The final image was created through analysis of 56 images and several computer-aided evaluation steps.

3D view of variable rotation

The result is 3D graphics showing the direction of rotation and magnetic energy in different regions of Skyrmion. Among other things, they show how the spins of neighboring atoms behave at the center and when moving to the edge of the magnetic vortex, and allow conclusions to be drawn about the physical interactions that prevail.

Using the data, physicists were also able to determine how the shape and three-dimensional structure of the skyrmion changed with radius and thickness. “A larger Skyrmion with a wider domain wall has a greater number of spins that follow the asymmetric interaction,” Raftery and his team explain. “For a skyrmion with a thin domain wall, the spins are more vertical, following out-of-plane anisotropy.”

New possibilities for spintronics

According to the physicists, their 3D examination of skyrmions now allows more detailed research into these magnetic nanostructures, thus paving the way for their future use as nanomemories or qubits. “Our results form the basis for nanometering technology for spintronic devices,” explains lead author Peter Fischer of Berkeley Lab.

This opens new possibilities for adapting these topological spin structures to the desired function. (Scientific Progress, 2024; doi: 10.1126/sciadv.adp8615)

Source: Science Advances, Lawrence Berkeley National Laboratory (Berkeley Lab)

October 28, 2024 – Nadia Podbrigar