Controlling the Size and Helicity of an Electron Magnetic vortex “Skyrmion”

RIKEN (President: Ryoji Noyori), the University of Tokyo (President: Junichi Hamada) and the National Institute for Materials Science (NIMS; President: Sukekatsu Ushioda) revealed that the size and helicity of a skyrmion, a magnetic structure consisting of electron spins arranged in a vortex shape, can be controlled by changing the concentration ratio of manganese and iron in Mn₁-_xFe_xGe. This finding provides an important guide to realizing power-saving magnetic memory devices using skyrmions as recording bits. The research result was achieved by a joint research group led by Dr. Yoshinori Tokura, Director of the Center for Emergent Matter Science (CEMS) and Group Director of the Strong Correlation Physics Research Group of CEMS, Mr. Kiyou Shibata, a graduate student, Dr. Koji Kimoto, Unit Director of the Surface Physics and Structure Unit, Advanced Key Technologies Division of NIMS, and their collaborators.

Electrons within a material have a spin which is a source of magnetism. Current magnetic memory devices, including hard disks, that use magnetic structures consisting of electron spins as recording bits can retain information without a power supply, but their processing speed is slow. Thus, research has been actively conducted to manipulate magnetic structures by electric current. Skyrmions can be driven by very small currents about five orders of magnitude smaller than other magnetic structures. Therefore, they are expected to be applied to high-speed, power-saving magnetic memory devices. However, before they can be integrated into devices and used, it is necessary to develop methods for controlling their size and helicity (the direction of their vortex).

The joint research group observed skyrmions in Mn₁-_xFe_xGe compounds with different concentration ratios of manganese and iron. As a result, the group revealed that the skyrmion size and the period of its helical magnetic structure change continuously up to approximately 5–200 nm (nanometers), and that the helicity of the skyrmion reverses when the concentration ratio of manganese and iron is about 1:4. These results suggest that the relativistic effect called ”spin-orbit coupling” decides the size and helicity of skyrmions.

This research was conducted as part of the “Quantum Science on Strong Correlation” project (Core Researcher: Yoshinori Tokura) of the Funding Program for World-Leading Innovative R&D on Science and Technology (FIRST), and the research results will be published in the online edition of the science journal, Nature Nanotechnology, on September 8 (September 9 JST).