World’s First Successful Direct Observation of “Vortex-shaped Spin Texture: Skyrmion Crystal”

As part of the JST Targeted Basic Research program, Prof. Yoshinori Tokura of the University of Tokyo, School of Engineering and a team headed by NIMS Researcher Xiuzhen Yu in the JST’s Exploratory Research for Advanced Technology (ERATO) research project, “Tokura Multiferroics Project,” succeeded in the world’s first real-space observation of a new spin texture called a “skyrmion crystal.” This spin texture is a skyrmion crystal in which skyrmions consisting of a large number of spins arranged in a vortex shape are placed regularly in a hexagonal lattice form. Because the spins have a spiral configuration in a skyrmion crystal, it is thought that large physical interaction occurs in both electricity and magnetism. Based on this distinctive structure, the occurrence of a gigantic anomalous Hall effect (several 10 to several 100 times that of semiconductor Hall devices currently in practical use) has been foreseen in these crystals. Future development of applications as materials having new physical properties that had not existed in the past is expected, beginning with application to high-sensitivity magnetic sensor devices for use in hard-disk drives and similar technologies. However, until now, the existence of skyrmion crystals had only been predicted indirectly under extremely limited cryogenic temperatures, and the mechanism responsible for their occurrence was not well understood.

In this work, the research group focused on Fe_0.5Co_0.5Si having a spiral spin texture, and succeeded for the first time in real-space imaging of a skyrmion crystal using a Lorenz transmission electron microscope. The group found that, under a weak magnetic field of only several 100 Gauss, this skyrmion crystal exists over a wide temperature range (from 5K to 30K) and is also comparatively stable. These results of skyrmion observation are in good agreement with the results of theoretical studies. By having confirmed the model of the mechanism responsible for the occurrence of skyrmions, this achievement will make it possible to fabricate various skyrmion crystals in the future, and thus opens the way to the creation of new functional substances.

JST Exploratory Research for Advanced Technology (ERATO) Type Research in Basic Research Program
 
Project Name: “Tokura Multiferroics Project”
Research Director: Yoshinori Tokura (Professor, University of Tokyo, School of Engineering)
Research Term: FY2006-2011
 
Through this project, the JST is pioneering new groups of materials by the discovery of new design guidelines for materials in combination with advanced monodzukuri (Japanese manufacturing) methods, based on a comprehensive approach encompassing the creation of multiferroic substances having strong electric-magnetic interaction and the construction of theories which explain the physical properties of those substances.