By monitoring the behavior of tiny magnetic vortices, RIKEN researchers have taken a step closer to developing low-energy devices based on spintronics.
Currently, traditional electronics, which involves shunting electric charges around circuits, is the foundation of all information technologies. But electrons also possess another feature called spin, which can be used to create faster and more effective devices.
The RIKEN Center for Emergent Matter Science’s Hazuki Kawano-Furukawa and her colleagues are spearheading efforts to advance this area of spintronics. Specifically, they are investigating the application of skyrmions, which are nanoscale magnetic whirlpools.
Skyrmions can be controlled with significantly smaller currents or electric fields. This makes them highly promising for future applications in information and communication technologies, such as computer memory that doesn’t need power to keep stored data.
Hazuki Kawano-Furukawa, Principal Investigator, RIKEN Center for Emergent Matter Science
The group concentrated on manganese monosilicide, sometimes known as a helimagnet, because of the helical patterns formed by the spin alignment in its molecular lattice. Measuring the lowest energy magnetic excitations in the skyrmion states required a highly sensitive apparatus.
Kawano-Furukawa added, “The only method that fulfills both the spatial and energy resolution requirements for this purpose is the neutron spin echo technique. 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 measures the effect of the sample’s magnetic fields on the spin and velocity of neutrons after illuminating it with a neutron beam.
The group’s data supported theoretical predictions that an asymmetric dispersion of excitations in the manganese monosilicide lattice is caused by the string-like structures of skyrmions. These excitations, according to Kawano-Furukawa, “know” whether they are moving parallel or antiparallel to the skyrmion whirlpool cores. This theoretical validation paves the path for more effective use of skyrmions.
It took the team two years to validate their findings.
“We conducted our initial experiment in October 2018. 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,” Kawano-Furukawa stated.
The group now plans to investigate the development of magnetic skyrmions in more detail.
Kawano-Furukawa concluded, “We aim to investigate the coexistence of the conical and skyrmion phases in manganese monosilicide.”
Soda, M., et al. (2023) Asymmetric slow dynamics of the skyrmion lattice in MnSi. Nature Physics. doi:10.1038/s41567-023-02120-5