Controlling size and helicity of a spin-vortex skyrmion
Towards power-saving spintronics memory devices
Graduate School of Engineering / Faculty of Engineering
Current magnetic memory devices such as the stripes on credit cards and computer hard disks store information using patterns of magnetic domains on magnetic media. These ferromagnetic domains are read and written, or altered, by applying an external electrical current. This technology underlies most computer storage systems today, but is limited by the size of the domains and the amount of current required. Magnetism results when the spins of electrons in a domain are aligned in the same direction, but recently scientists have discovered the skyrmion, which consists of electron spins arranged in a vortex structure, and can be driven or affected by very small currents about five orders of magnitude smaller than standard ferromagnetic domains. As a result, it is seen as a potential candidate for a data carrier in the next-generation of high-speed and low-energy magnetic storage devices. However, before they can be used in such spintronics devices, it is necessary to develop methods for controlling skyrmions’ size and helicity (the direction of their vortex).
Prof. Yoshinori Tokura at the Graduate School of Engineering of the University of Tokyo, graduate student Kiyou Shibata, and their collaborators have observed and analyzed a series of Mn1-xFexGe compounds by transmission electron microscopy. They have revealed that the size of the skymions changes continuously as a function of composition, and the helicity of the skyrmion reverses at a certain composition (x ～ 0.8). These results suggest that the size and helicity of skyrmions can be tuned through the strength of spin-orbit coupling by changing composition of the substrate material. This mixed-crystal approach may pave the way for developing spintronic devices utilizing skyrmions.
Kiyou Shibata, Xiuzhen Yu, Toru Hara, Daisuke Morikawa, Naoya Kanazawa, Koji Kimoto, Shintaro Ishiwata, Yoshio Matsui, and Yoshinori Tokura,
“Towards control of the size and helicity of skyrmions in helimagnetic alloys by spin-orbit coupling”,
Nature Nanotechnology Advanced Online Publication: 2013/9/9 AM 2:00(Japan time), doi: 10.1038/NNANO.2013.174.