A cryo-Lorentz TEM is a powerful tool to directly and quantitatively characterize magnetic structures at a controlled temperature (6 ~ 300 K) and with a high spatial resolution (< 2 nm). In addition, the dynamic behaviors of the magnetic domains in the course of the magnetic phase transition under an external field can be acquired by in-situ Lorentz TEM observation for the nanometric magnetic structures.

Recently, we clarified the spatial fluctuation of magnetic structures and modulated crystal structures in a colossal anisotropic-magnetoresistance (AMR) material La0.69Ca0.31MnO3 [1]: the long-range spin ordering structure in the (001) plane collapses into the short-range charge/orbital ordering (CO/OO) state; changes in the magnetic domain structure with an external magnetic field demonstrate the pinning effect of twin boundaries on a magnetic domain wall, which may enhance the AMR [2].

Another topic is the realization and manipulation of a topological spin object - skyrmion. The skyrmion is promising for applications for spintronics due to its nontrivial electric and magnetic phenomena including the topological Hall effect (THE). We have successfully visualized and manipulated such nanometric skyrmions in helimagnets [3-5] by using cryo-Lorentz TEM. The critical current J_C for driving skyrmions is less than 100 A/cm2 [6], several orders of magnitudes lower than that for driving magnetic domain walls in ferromagnets. These findings will open a door to less energy-consumption skyrmion-based devices toward next-generation spintronics. Collaborators of the above studies include Prof. Yoshinori Tokura, Prof. Naoto Nagaosa, Dr. Yoshio Matsui, Prof. Yoshinori Onose, Mr. Naoya Kanazawa, Dr. S. Seki, Prof. Run-wei Li, Dr. Koji Kimoto, Dr. Toru Asaka, Dr. Toru Hara, Dr. Takuro Nagai, and Ms. Weizhu Zhang. [1] R-W. Li, et al., Proc. Nat. Acad. Soc. 106, 14224 (2009). [2] X. Z. Yu, et al. Appl. Phys. Lett. 95, 092504 (2009). [3] X.Z. Yu, et al., Nature 465, 901 (2010). [4] X. Z. Yu, et al., Nature Materials 10, 106 (2011). [5] S. Seki, et al., Science 336, 198 (2012). [6] X. Z. Yu, et al., Nature Communications, in press.

报告人介绍：Dr Yu obtained her doctorate in physics from 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 then joined the 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. Now, she is focusing on the realization and manipulation of nanometric spin textures – skyrmions, in the Institute of Physical and Chemical Research (RIKEN), Japan.