Researchers from Japan's RIKEN Center for Emergent Matter Science (CEMS) and Ochanomizu University, UK's University of Birmingham, Sweden's Lund University, Canada's Université de Sherbrooke, Czech Republic's Nuclear Physics Institute, France's Institut Max von Laue-Paul Langevin (ILL) have advanced low-energy devices based on spintronics, by measuring the dynamics of tiny magnetic vortices.
The team examined the low-energy excitations of the skyrmion state in MnSi by using the neutron spin-echo technique under small-angle neutron scattering conditions. The scientists observed an asymmetric dispersion of the phason excitations of the lattice because of the string-like structure of the skyrmion cores.
The researchers pushed forward spintronics technology by studying the dynamics of magnetic vortices, offering potential for more efficient low-energy devices.
The study focuses on the nanoscale magnetic whirlpools called skyrmions, which require less energy to control, promising advancements in data storage and ICT.
Experiments at the Institut-Laue-Langevin, using the IN15 neutron spin echo spectrometer, were key to observing skyrmion behavior in manganese monosilicide.
The findings confirm theoretical predictions about skyrmions, potentially paving the way for their practical application in information technologies.
The team focused on the material manganese monosilicide—a helimagnet, so-called because the spins in its molecular lattice align in helical patterns. Extremely sensitive equipment was necessary to measure the lowest energy magnetic excitations in the skyrmion states.
“The only method that fulfills both the spatial and energy resolution requirements for this purpose is the neutron spin echo technique,” says RIKEN's Hazuki Kawano-Furukawa. “We conducted experiments using the state-of-the-art IN15 neutron spin echo spectrometer at the Institut-Laue-Langevin in Grenoble, France. This instrument boasts the highest performance in the world for studying the dynamics of materials in magnetic fields.”
The spin echo method works by illuminating a sample with a beam of neutrons, and measuring how the sample’s magnetic fields affect the spin and velocity of the neutrons.
Through their observations, the team verified theoretical predictions that the string-like structures of skyrmions cause an asymmetric dispersion of excitations in the lattice of manganese monosilicide. As Kawano-Furukawa explained, these excitations ‘know’ if they are traveling parallel or antiparallel to the cores of the skyrmion whirlpools. This confirmation of theory opens up the way to better exploit skyrmions.
The team had to wait two years to confirm their results. “We conducted our initial experiment in October 2018,” she says. “However, to draw final conclusions, we needed to confirm that the behavior was observed only in the skyrmion phase, and not in another magnetic structure called the conical phase. Due to the COVID-19 pandemic, the follow-up experiment was postponed to January 2021 and was carried out remotely, posing various challenges.”
The team now intends to conduct further research on how magnetic skyrmions are generated. “We aim to investigate the coexistence of the conical and skyrmion phases in manganese monosilicide,” says Kawano-Furukawa.