ABSTRACT
Nitrosyl metal complexes (M-NO), in which nitrosyl ligands are coordinated to transition-metal ions, have been studied from the viewpoints of physiological activity, catalytic activity, and photosensitivity. The structural flexibility and electric polarization of the nitrosyl ligand are attractive characteristics. Herein we show a photoswitchable nonlinear-optical (NLO) crystal based on a dysprosium-iron nitrosyl assembly. This crystal is composed of a one-dimensional chain structure in the polar Pna21 space group. Because of spontaneous electric polarization, it exhibits a NLO effect of second harmonic generation (SHG). The SHG signal reversibly changes by alternate irradiation with 473 and 804 nm laser lights. The observed photoreversible switching effect on SHG is caused by photoinduced linkage isomerization of the metal nitrosyl sites, i.e., M-N+âO â M-OâN+. Such an optically switchable NLO crystal should be useful for optical devices such as optical filters and optical shutters as well as probes in SHG microscopy.
ABSTRACT
Ionic conductors serve as solid electrolytes for fuel cells and batteries, whereas polar crystals such as ferroelectrics and pyroelectrics-which are typically insulating materials-are used in electronic devices. Here we show a material that combines superionic conductivity with a polar crystal structure at room temperature. This three-dimensional anionic network is based on -Fe-N≡C-Mo- units, with Cs cations hosted in every other pore. In the resulting Cs1.1Fe0.95[Mo(CN)5(NO)]·4H2O material, the negative and positive charges of the framework and Cs+ ions, respectively, are non-symmetrically shifted in the c-axis direction of the unit cell, and spontaneous electric polarization is generated, in turn leading to second harmonic generation (SHG). Additionally, this material is a superionic conductor (with an ionic conductivity value of 4 × 10-3 S cm-1 at 318 K). Furthermore, the ionic conductivity significantly decreases under 532 nm light irradiation (from 1 × 10-3 S cm-1 to 6 × 10-5 S cm-1 at room temperature) and, when irradiation stops, returns to its original value within ~1 h.
ABSTRACT
Development of nanometer-sized magnetic particles exhibiting a large coercive field (Hc) is in high demand for densification of magnetic recording. Herein, we report a single-nanosize (i.e., less than ten nanometers across) hard magnetic ferrite. This magnetic ferrite is composed of ε-Fe2O3, with a sufficiently high Hc value for magnetic recording systems and a remarkably high magnetic anisotropy constant of 7.7 × 10(6) erg cm(-3). For example, 8.2-nm nanoparticles have an Hc value of 5.2 kOe at room temperature. A colloidal solution of these nanoparticles possesses a light orange color due to a wide band gap of 2.9 eV (430 nm), indicating a possibility of transparent magnetic pigments. Additionally, we have observed magnetization-induced second harmonic generation (MSHG). The nonlinear optical-magnetoelectric effect of the present polar magnetic nanocrystal was quite strong. These findings have been demonstrated in a simple iron oxide, which is highly significant from the viewpoints of economic cost and mass production.
