90-degree optical switching of output second-harmonic light in chiral photomagnet

Optical control of physical properties and functionalities is an attractive area of research in the development of advanced optical materials. Here, we report a magnet that can switch the polarization plane of light by 908 under optical stimulation. The magnet is a chiral structured iron-octacyanoniobate, and its magnetic properties can be reversibly switched by irradiating with blue and red light, which causes light-reversible spin-crossover on the iron(II) ion. Using this material, second-harmonic generation, a nonlinear optical effect, was investigated. The vertical polarization plane was switched to horizontal polarization by irradiating with blue light, and was then returned to the original vertical polarization by irradiating with red light. This phenomenon originates from alternate optical switching between crystallographic and magnetic contributions to second-harmonic generation within the magnet, where the chiral structure and photomagnetism are coupled. The observed perpendicular optical switching should encourage studies in the fields of magneto-optical memory and optoelectronic devices.