A difficult-to-describe nanoscale object called the magnetic skyrmion might one day yield new microelectronic devices that can do much more -; for example, massive data storage -; all while consuming much less power.
But researchers need a more detailed understanding of skyrmions if they are ever to be used reliably in computational devices, including quantum computers. Peter Fischer, a senior researcher at the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab), led a project to make 3D X-ray images of skyrmions that can characterize or measure the orientations of spins inside the whole object. "Our results provide a foundation for nanoscale metrology for spintronics devices," Fischer said. The work was recently published in Science Advances.
Magnetic skyrmions can be thought of as spinning circles of magnetism, explains David Raftrey, a student researcher in Fischer's team who was the lead author of this study. At the center, the magnetic spin is pointing upward, while moving out from the center, the magnetism twists and pulls in a downward direction. What's more, skyrmions are stable, small, fast, and not easily unfolded, a trait materials scientists dub "topological."
These spin directions are part of the appeal for skyrmions because they might be used to carry and store information in much the same way that electrons carry and store information in current devices. "However, relying on the charge of the electron, as it is done today, comes with inevitable energy losses. Using spins, the losses will be significantly lower," Fischer said.
But theoretical knowledge of skyrmions has been based on descriptions of them as 2D objects. In the real world of electronics and silicon wafers -; no matter how thin -; skyrmions have to be dealt with as 3D objects. To put skyrmions to work, or perhaps to one day synthesize custom skyrmions, researchers must be able to examine and understand their spin characteristics throughout the whole 3D object.
If you are looking at a skyrmion magnetic whirlpool from the top and start slicing off layers, you might think that each successive layer would be the same. "But that's not the case," Raftrey said. "And we said, okay, how can we get our arms around this- How do we actually demonstrate this-"
Raftrey took a thin magnetic layer, which was synthesized by colleagues from Western Digital, and patterned a nanodisk using the Molecular Foundry's nanofabrication facility. To obtain 3D tomographic images he traveled to Switzerland to use a novel imaging technique called magnetic X-ray laminography at a microscopy beamline at the Swiss Light Source.
With X-ray laminography, "You can basically reconfigure and reconstruct [the skyrmion] from these many, many images and data," Raftrey said. It was a process that took months, finally yielding a better understanding of skyrmion spin structures.
A full understanding of skyrmions' 3D spin texture "opens opportunities to explore and tailor 3D topological spintronic devices with enhanced functionalities that cannot be achieved in two dimensions," Fischer said.
The Molecular Foundry is a DOE Office of Science user facility at Berkeley Lab.
The work was supported by the DOE Office of Science.