Japan Atomic Energy Agency, Japan
KK has completed his Ph.D from TU Berlin working a the Hahn-Meitner Institut, Berlin. He joined the Institute for Solid State Physics of the University of Tokyo as an assistant professor and became a professor in 1997. He was the Director General of the QuBS Directorate at the JAEA until 2014 and now serves as a Senior Consultant in the QuBS Center, JAEA.
The recent development of neutron scattering techniques, especially polarized neutron scattering utilization, will be reported with examples from the recent investigations on mutiferroic materials. The recent discovery of the spin-driven ferroelectricity triggered intense exploration of new multiferroic materials and research of the novel magneto-electric effect in condensed matter. In studying these advanced functional materials, one is permanently confronted with complex spin configurations, for example, non-collinear, incommensurate magnetic structure such as helimagnetic or cycloidal spin structure as a result of frustrated magnetic interactions. Since the giant functional responses in these materials are direct consequences of these complex magnetic structures breaking the inversion symmetry, the detailed knowledge of the spin structure is mandatory to understand the essence of these advanced magnetic functional materials. More recently an electric-dipole-active magnetic excitation, often termed as electromagnon, has been observed in these multiferroic materials. The polarized neutron technique, in addition to the conventional unpolarized neutron scattering, can greatly contribute to obtain deep insight into these complex spin structures and excitations. The examples include investigations on ferroelectricity induced by a proper screw-type helical spin ordering in Ga-doped CuFeO2 and electromagnon in the Y-type hexaferrite Ba2Mg2Fe12O22 with transverse conical spin structure. These investigations were performed in collaboration with S. Wakimoto and M. Takeda, Quantum Beam Science Center, Japan Atomic Energy Agency, Japan; T. Nakajima, T. Arima, Y. Taguchi, Y. Tokunaga, Y. Kaneko and Y. Tokura, Center for Emergent Matter Science, RIKEN, Japan, N. Terada and H. Kitazawa, National Institute for Materials Science, Japan; S. Mitsuda, Dep. of Physics, Tokyo University of Science, Japan; S. Ishiwata, Department of Applied Physics, University of Tokyo, Japan; D. Okuyama, IMRAM, Tohoku University, Japan ; M. Matsuda and J. Fernandez-Baca, Quantum Condensed Matter Division, Oak Ridge National Laboratory, USA.