学 术 报 告

报告题目：Visualization of nanometric magnetic vortex (skyrmion) by TEM
报告人： Dr. Xiuzhen Yu (The Institute of Physical and Chemical Research (RIKEN，Japan)
时 间： 2012年1月5日（星期四） 上午9:30
地 点： 强磁场中心磁体准备间201会议室
摘 要：The skyrmion, a vortex-like spin object was anticipated by a nuclear physicist Tomy Skyme 50 years ago. It was a puzzle until the recent small-angle neutron scattering experiments for a helical magnet MnSi. Such neutron studies indicated the generation of skyrmion lattice under a specific condition of temperature (T) and magnetic external field (B). However, the reciprocal-space study is difficult to clarify the aspect of individual skyrmion and also dynamic skyrmions. In this study, we perform the real-space observations to provide more direct and complementary information for the skyrmion structure by the means of Lorentz transmission electron microscopy (TEM). The target compounds are Fe0.5Co0.5Si and FeGe with the non-centresymmetric crystal structure. The formation process of two-dimensional (2D) skyrmion crystal (SkX) and the related phase diagram in 20 nm-thick Fe0.5Co0.5Si film are revealed. These results indicate that SkX is much more stable in 2D thin film than in 3D bulk. Furthermore we report on the near room-temperature formation of SkX in FeGe. This is the first time to observe SkX with a formation temperature as high as ~ 280 K. We have clarified the stability condition for SkX, i.e. the magnetic-dimension (from 2D to 3D) variation of SkX phase diagram in (T, B)-plane. The room-temperature stable SkX demonstrated by this study is important for the materials design toward the development of skyrmion-based devices.
报告人简介：
Dr Yu completed her doctorate in physics with the characterizations of crystal and magnetic structures of transition metal oxides by using transmission electron microscopy (TEM) at Tohoku University in 2008. She worked in Tokura spin superstructure (SSS) project (Japan Science and Technology Agency) in 2002-2006, in charge of microstructure characterization using TEM. She collaborated with Tokura team and found the novel electrical-magnetic phenomena such as variation of charge/orbital ordering structure, temperature-induced spin reorientation and the pinning effect of crystal defects on the magnetic domains in transition metal oxides. After Tokura SSS project, she joined Advanced Electron Microscopy Group in the National Institute of Materials Science (NIMS) to develop a micro-calorimeter type X-ray detection system for TEM in 2006-2010. This work made the realization of a TEM-oriented high resolution (~10 eV) energy dispersive X-ray spectrometer (EDS) for the first time. From 2010 to 2011, she jointed Tokura group in the Institute of Physical and Chemical Research (RIKEN) and made an effort to realize the nano-scale spin texture of vortex-like skyrmion as well as helical spin structure. She and her collaborators successfully visualized the two-dimensional spin texture of skyrmion in helimagnets Fe0.5Co0.5Si and FeGe. This technology should be capable to pave a new path to devise the skyrmion-based magnetic random access memory, in which information is stored in nano-scale skyrmions.