A powerful, custom-built X-ray microscope at the Department of Energy's SLAC National Accelerator Laboratory was used by researchers to directly observe the magnetic version of a soliton, a type of wave that can travel without resistance. Magnetic solitons are quite stable and can maintain their shape and strength as they travel across a magnetic material. In experiments at SLAC’s Stanford Synchrotron Radiation Lightsource, researchers recorded the first X-ray images of solitons that were generated by hitting a magnetic material with electric current to create rippling magnetic effects.

Results from the two independent experiments were published Sept. 17 in Physical Review Letters and Nov. 16 in Nature Communications.

“Magnetism has been used for navigation for thousands of years and more recently to build generators, motors and data storage devices,” said co-author Hendrik Ohldag. “However, magnetic elements were mostly viewed as static and uniform. To push the limits of energy efficiency in the future we need to understand better how magnetic devices behave on fast timescales at the nanoscale, which is why we are using this dedicated ultrafast X-ray microscope.”

Leading author Stefano Bonetti added: "We built a microscope that allowed us to look at these magnetic waves in a new way. With this new microscope, we can actually see them moving. We can see things directly." An ultra-fast camera attached to the microscope enabled researchers to capture six images that were compiled in sequence to form a “mini movie” of the soliton’s movements. It took some 12 hours to record enough X-ray data to create the clip.

Stefano Bonetti/Stockholm University

Solitons are a form of spin waves - disturbances that propagate in a magnetic material as a patterned, rippling effect in the material’s electrons. This response is related to the spin of electrons, a fundamental particle property. For decades, solitons have been theorized to occur in magnets, but it took a specialized X-ray microscope like the one at SLAC to directly observe the effect.

Since solitons can move without resistance and are remarkably stable, scientists are exploring whether these magnetic waves can be used to carry and store information in a new and more efficient form of computer memory, one that needs less energy and generates less heat. Future advanced materials using soliton properties would be a tremendous advantage over current materials used in modern electronics, which require more energy to move data due to resistance and which causes them to heat up.

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