Department of Advanced Materials Science, University of Tokyo
5-1-5 Kashiwanoha, Kashiwa, Chiba 277-8561, Japan
Tel/Fax: +81-4-7136-3752; e-mail: tkimura@edu.k.u-tokyo.ac.jp
Tsuyoshi Kimura received his Ph.D degree from University of Tokyo in 1996. From 1996 to 2000, he was at Joint Research Center for Atom Technology at Tsukuba, Japan, as a postdoctoral fellow. Subsequently, he was a lecturer at Department of Applied Physics in University of Tokyo between 2000 and 2003. He worked as a Limited Term Staff Member from 2003 to 2005 in Los Alamos National Laboratory and as a Member of Technical Staff in Bell Laboratories, Lucent Technologies from 2005 to 2007. He became a professor of Graduate School of Engineering Science, Osaka University in 2007, and moved to the present institute (Department of Advanced Materials Science, University of Tokyo) in 2017.
He has extensive research experience in the single-crystal growth of transition-metal oxides (e.g., high- and low-Tc superconductors, magnetoresisitive oxides, magnetoelectric multiferroics, and frustrated spin systems) and in the characterization of structural, magnetic, and electric properties of these materials. So far, he has discovered several fascinating functionalities (e.g., giant tunneling magnetoresisitance, giant magnetoelectric and magnetocapacitive effects) in the research of materials science. Especially, he and his coworker discovered a number of new multiferroic materials.
The symmetry breaking ascribed to the evolution of an order parameter is one of the most important concepts in materials physics. Representative examples are symmetry breakings in “ferroic” materials such as the symmetry breaking of time reversal in ferro-magnets and that of space inversion in ferro-electrics. Thus, one can find that this concept contributes to not only fundamental science but also materials’ functionalities available for device applications. Furthermore, recent research developments of “multiferroic” materials with broken time-reversal and space-inversion symmetries have triggered extensive studies on unconventional ferroic materials such as “ferro-toroidic” and “ferro-axial” materials.
In the case of ferro-toroidal order whose order parameter is a toroidal moment, that is, the sum of the cross product of spin and its position vector. Most typically, the toroidal moment is generated by head-to-tail arrangement of magnetic dipoles, which breaks both the time-reversal and space-inversion symmetries. When we replace magnetic dipoles in toroidal moment with electric dipoles, ferro-axial moment is generated. In the ferro-axial order, a rotational electric-dipole arrangement breaking some mirror symmetry, the so-called ferro-axial moment, is an order parameter.
In this presentation, we show symmetry-dependent magnetic, electric, and optical phenomena characteristic of unconventional ferroic orders such ferro-toroidal, ferro-axial, and ferro-quadrupole orders. The phenomena include magnetoelectric effect, nonreciprocal directional dichroism, and electrogyration. Furthermore, in general, ferroic materials bear “domain” structures, that is, spatial distributions of order parameters. However, observations of domain structures in unconventional ferroic materials are not straightforward. Here, we also show ways to spatially visualize domain structures in such unconventional ferroic materials.