90-degree optical switching of output light in the first chiral photomagnet
Discovery of novel magneto-optical switching
Graduate School of Science / Faculty of Science
Materials that exhibit optical change in the physical properties, especially “photomagnets”, whose magnetic properties can be directly changed by light (optically switched), are greatly desired since their magnetic properties could be controlled without external magnetic field, heat, or physical contact.
Prof. Shin-ichi Ohkoshi’s research group at the Department of Chemistry, Graduate School of Science, the University of Tokyo, has discovered a novel phenomenon, where the polarization plane of the output light from the material is reversibly switched between horizontal and vertical, by introducing chirality into a photo-responsive magnet.
The research group developed a new chiral structured magnet, where iron (Fe) ions and niobium (Nb) ions are three dimensionally bridged by cyano groups (?CN?). By alternatively irradiating with blue light (wavelength: 473 nanometers) and red light (wavelength: 785 nanometers), the magnetization of the material can be reversibly switched (hereafter, we call this new magnet a chiral photomagnet). Using this chiral photomagnet, the research group investigated second harmonic generation (a phenomenon where an input light with a particular wavelength is converted to an output light with half the wavelength), one of the nonlinear optical effects. As a result, at a nonmagnetic state before light irradiation, input light with a horizontal polarization plane was converted to an output light with a vertical polarization plane. However, when the sample was transformed into a magnetic state (photomagnetic state I) by irradiating with blue light, an output light with a horizontal polarization plane was observed. Furthermore, when irradiated with red light to generate a magnetic state with weak magnetization (photomagnetic state II), the polarization plane of the output light was returned to vertical. In this way, the research group succeeded in 90-degree switching of the polarization plane of the output second harmonic light by changing the state of the magnet with blue and red light. There have not been any other reports of chiral photomagnets, and this is the first successful example in the world. With the development of such a novel material, chirality and magnetic properties were coupled to exhibit 90-degree switching of the polarization plane of the output light. This switching phenomenon, which is totally different from the conventional Faraday effect, was achieved by combining the cutting-edge technologies of optical science and material science. These findings are expected to be applied in optical memory devices, optical sensors, and optical communication technology (S. Ohkoshi et al., JP2013-209102).
This work was supported by the Core Research for Evolutional Science and Technology (CREST) project of Japan Science and Technology (JST) in the “Development of high-performance nanostructures for process integration” research area (research supervisor: Masahiro Irie) with a research theme of “Bottom-up synthesis of innovative functional nanomaterials based on magnetochemistry” (principal investigator: Shin-ichi Ohkoshi). The article was published as an advanced online article on the British science journal Nature Photonics on November 24, 2013 (Sun) at 6 p.m. London time.
Press release (Japanese)
S. Ohkoshi, S. Takano, K. Imoto, M. Yoshikiyo, A. Namai, H. Tokoro,
“90-degree optical switching of output second-harmonic light in chiral photomagnet”,
Nature Photonics Published online: 2013/11/25 (Japan time), doi: 10.1038/NPHOTON.2013.310.