Published papers

The magnetic properties and photo-magnetic effects of the electrochemically prepared metal polycyanide film, Fe1.5II[CrIII(CN)6]·7.5H2O, were investigated. Magnetization measurements showed that it was a ferromagnet (parallel spin ordering) having a Tc = 21 K. The spontaneous magnetization decreased optically by the photoexcitation of the intervalence transfer (IT) band between FeII and CrIII. This optically reduced magnetization persisted for a period of several days at 5 K after turning off the light. 57Fe Moessbauer experiments showed that the spin state of iron did not change but the strength of a ferromagnetic interaction between FeII and CrIII decreased after the irradiation, forming a paramagnetic metastable state. This metastable state returned to the original state above 40 K, showing that the magnetization of this compound can be controlled reversibly by the combination of optical and thermal methods.

The intercalation of inorganic materials into organized organic assemblies presents many opportunities for the development of new functional materials with superior physicochemical properties. We have designed a composite material comprising Prussian blue intercalated into photoresponsive organic molecules (azobenzene-containing multibilayer vesicles). Photoisomerization in the solid system was achieved by diluting the azobenzene-containing bilayer membrane in a poly(vinyl alcohol) matrix. The photoisomerization of the film was accompanied by a geometrically confined structural change within the vesicles, as reflected by changes in the dipole moment and electrostatic field. As a result, we were able to control the magnetic properties of this material by photoillumination.

The electronic states of Fe atoms in Co[Fe(CN)5NH3]·xH2O were studied by means of 57Fe Mössbauer spectroscopy. The Mössbauer spectra of Co[Fe(CN)5NH3]·6H2O show the coexistence of mixed valences for the Fe atoms and a magnetic relaxation at 4 K. When water molecules were removed, electron transfer from Co to Fe occurred.

We studied the external magnetic field effects on the photoinduced magnetization of a cobalt iron cyanide, K0.4Co1.3[Fe(CN)6]·5H2O. Photoinduced magnetization value was increased ca. 20 % at maximum under the magnetic field of 50000 G at 5 K. In addition, in the ferrimagnetic region (T < Tc = 26 K), the external magnetic field accelerated the rate of photoinduced spin generation. Those data suggest that external magnetic field increases magnetic interaction between the excited state and spin clusters.

Unstable novel species produced by photolysis of ferrocene (Cp2Fe) isolated in low-temperature matrix were studied by means of the 57Fe Mossbauer spectroscopy. On the UV-irradiation of 57Fe-enriched ferrocene co-condensed with CCl2 in low-temperature N2 matrix (20 K), unknown high spin ferrous species (I.S. = 0.90 ± 0.02 mm/s), Q.S. = 1.94 ± 0.02 mm/s) were produced as well as ferricinium ion [Cp2Fe]+ (I.S. = 0.52 ± 0.01 mm/s, Q.S. = 0.0 mm/s). On the annealing, these photoproducts disappeared to reform ferrocene by the reverse reaction in the matrix. The mechanisms of the photochemical reaction were discussed.

The electronic states of cobalt iron cyanides were observed using 57Fe Mössbauer. It was revealed that Prussian blue analogs Co1.5[Fe(CN)6]6H2O and K0.5Co1.25[Fe(CN)6]3.6H20 have FeIII(low spin) and FeII(low spin), respectively, at both room temperature and 4 K. In Co1.5[Fe(CN)6]6H2O, a magnetic hyperfine interaction was observed at low temperature. Moreover, the Mössbauer spectra provided clear evidence for an internal electron transfer from FeII to CoIII in K0.5Co1.25[Fe (CN)6]3.6H2O by red light illumination at low temperature.

The electronic structure of a cobalt iron cyanide thin film, Na0.4Co1.3[Fe(CN)6]5H2O, was switched from FeIII(low spin)-CN-CoII(high spin) to FeII(low spin)-CN-CoIII(low spin) by exchanging cations in interstitial sites from Na+ to K+. The reverse process was also induced by replacing Na+ with K+. That is, the alkali cations in the interstitial sites dominate the electronic and spin states of the host compound. This type of switching phenomenon can be achieved by choosing a compound with both electronic degeneracy and zeolitic properties.

Reversible photoinduced magnetization was observed in a cobalt iron cyanide thin film. Magnetic properties of the prussian blue analog, K0.4Co1.3[Fe(CN)6] ·5H2O, can be switched between ferrimagnetic and paramagnetic by visible and near-IR light illumination.The critical temperature after illumination was about 26 K. This material, obtained via an electrochemical route in the form of thin films on an electrode, provides a new system whose magnetic properties can be controlled by both photochemical and electrochemical redox reactions.