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 × 106 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.

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Chiral and achiral three-dimensional cyanido-bridged metal assemblies with 4-halopyridine, [MnII(4-Xpy)4]2[NbIV(CN)8] (X = I, 1; X = Cl, 2), are prepared. 1 and 2 show ferrimagnetism with TC of 22 and 28 K, respectively. Chiral compound 1 exhibits second-harmonic generation.

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 Pna2 1 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 + O ↔ MON + . 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.

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