Minoru Kinoshita

Bulk ferromagnetism in the β-phase crystal of the p-nitrophenyl nitronyl nitroxide radical

Transition to a ferromagnetic long-range ordered state was found at 0.60 K in the orthorhombic β-phase crystal of p-nitrophenyl nitronyl nitroxide (or 2-(4′-nitrophenyl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl-3-N-oxide in the IUPAC nomenclature). This finding follows our recent discovery of the first organic bulk ferromagnet in the triclinic γ-phase crystal of the same compound.

Ferromagnetism of Organic Radical Crystals

Recently, the transition to ferromagnetic order has been found in crystals of organic compounds not containing metallic elements. The progress of the research is reviewed starting from the initial stage of study to obtain the design strategies to induce ferromagnetic interaction in organic crystals to the discovery of ferromagnetism in p-nitrophenyl nitronyl nitroxide ( p-NPNN; C13H16N3O4). The recent development in the field of molecular magnetism is also described.

Ferromagnetic coupling in a new phase of the p-nitrophenyl nitronyl nitroxide radical

Abstract The crystal structure of a new phase of the p -nitrophenyl nitronyl nitroxide radical compound is described. A study of its magnetic properties reveals the largest intermolecular ferromagnetic coupling reported so far among a series of polymorphs of this compound.

Ferromagnetic intermolecular interaction in the galvinoxyl radical: Cooperation of spin polarization and charge-transfer interaction

Abstract The orbital energies and the intermolecular overlap integrals of the galvinoxyl radical are calculated. It is found that the ferromagnetic intermolecular interaction in galvinoxyl can be qualitatively interpreted by a combined effect of spin polarization within the radical and charge-transfer interaction between the radicals.

Photofragmentation of mono‐ and dichloroethylenes: Translational energy measurements of recoiling Cl and HCl fragments

Translational energy (Et ) spectra of Cl and HCl fragments from vinylchloride, trans‐dichloroethylene, cis‐dichloroethylene, and 1,1’‐dichloroethylene have been measured for the π*←π excitation at 193 nm. Et distribution and angular dependence of the Cl fragment indicate that the two‐center dissociation occurs in a time faster than a rotation period and the recoiling organic radical (the counter fragment) is highly vibrationally excited. In dichloroethylenes, the presence of a second channel producing Cl atoms has been confirmed and attributed to the dissociation from the lower (n,σ*) state through a (π,σ*) state. The Et distribution of HCl fragments is nonstatistical and found to converge to null population at an energy less than half of the total available energy. This convergence point coincides with the value of the local available energy for the elimination reaction (activation energy —ΔH0reaction ). The yield of HCl molecules relative to Cl atoms is estimated to be ∼1.1 for vinylchloride. High effic...

Ferromagnetic intermolecular interactions in a series of organic mixed crystals of galvinoxyl radical and its precursory closed shell compound

The magnetic properties of the 4:1, 6:1, 9:1, and 19:1 mixed crystals of galvinoxyl (4‐[[3,5‐bis(1,1‐dimethylethyl)‐4‐oxo‐2,5‐cyclohexadien‐1‐ylidene]methyl]‐2,6 ‐bis(1,1‐dimethylethyl) phenoxy) radical and its precursory closed shell compound, hydrogalvinoxyl, have been studied. From the measurements of the temperature dependence of the magnetic susceptibility, it is found that the ferromagnetic intermolecular interactions, which are lost below about 85 K in pure galvinoxyl because of the phase transition, are maintained down to 2 K in these mixed crystals, and that the number of galvinoxyl radicals keeping the ferromagnetically coupled structure at low temperature increases as the concentration of hydrogalvinoxyl increases. The magnetic behavior of the mixed crystals at low temperature depends on the thermal history of the sample and is well interpreted by assuming the presence of a glassy state into which the high‐temperature, ferromagnetically coupled phase is quenched. The magnetization curves show t...

Semiconductive Properties of Tetracyanoethylene Complexes and Their Absorption Spectra

The absorption bands characteristic of the solid molecular complexes of tetracyanoethylene are attributed to the charge transfer interaction between tetracyanoethylene and donor molecules.In the complexes with polycyclic aromatic hydrocarbons the energy gap associated with the semiconductivity agrees well with the energy of the charge transfer excitation in the crystalline state, while the former is much smaller than the later in the complexes with polymethylbenzenes and azulene.

Electrical conductivity and superconductivity of metal phosphides with skutterudite-type structure prepared at high pressure

Abstract Metal phosphides with skutterudite (CoAs 3 )-type structure have been prepared using a wedgetype cubic-anvil high pressure apparatus. NiP 3 , LaRu 4 − x Os x P 12 ( x : 0, 1, 2, 3, 4) and CeRu 4 P 12 were synthesized at around 1100 °C and 4 GPa. The electrical conductivity and superconductivity of these metal phosphides were studied at low temperatures. The resistivity of NiP 3 was 1.6 × 10 −3 Ω cm at room temperature and decreased with decreasing temperature. A magnetic susceptibility of the phosphide showed Pauli paramagnetism. NiP 3 behaves as a metal. The resistivity of CeRu 4 P 12 increased with decreasing temperature. The semiconductive behavior was observed for this phosphide. The superconductivity of LaRu 4 P 12 , LaRu 3 OsP 12 and LaRu 2 Os 2 P 12 was observed at around 7 K. The magnetic field dependence of the T c was studied for LaRu 4 P 12 . The upper critical field ( H c 2 ) of LaRu 4 P 12 was 3.65 tesla at 0 K. The superconductivity of LaOs 4 P 12 was not found above 2 K. The electronic states and the superconductivity of the metal phosphides with skutterudite-type structure are discussed.

Organic radical clusters with ferromagnetic intermolecular interactions

Abstract The magnetic properties of the mixed crystal of galvinoxyl radical (2,6-di- t -butyl-4-(3,5-di- t -butyl-4-oxocyclohexa-2,5-dienylidenemethyl) -phenoxyl) and its precursory compound, hydrogalvinoxyl, in 6:1 ratio have been studied. The magnetic susceptibility of the mixed crystal follows the Curie-Weiss law in the range of 2–300 K with a positive Weiss constant of 7 K. Thus the ferromagnetic interactions are maintained over the whole temperature range in the mixed crystal, in contrast to the pure galvinoxyl in which the paramagnetism disappears below the phase transition temperature of 85 K. The magnetization curves for the mixed crystal measured at 2 and 5 K seem to follow closely along the theoretical curve for S = 3. The ferromagnetic interactions thus extend over six radicals on an average. However, the observed magnetization could more reasonably be explained by assuming an assembly of segments consisting of galvinoxyl radicals ferromagnetically coupled with each other and having various spin multiplicities in proportion to the segment size.

Growth of Large Isometric YBa2Cu3Ox Single Crystals from Coexisting Region of Solid with Melt in Y2O3 Crucibles

Large isometric single crystals of oxide superconductor YBa2Cu3Ox (YBCO) have been grown from a mixed region of solid Y2BaCuO5 and melt. The crystals possess sharp, shiny habits with a maximum thickness of about 7 mm along the c-axis. The best growth condition is that wherein the solvent composition is 7BaCuO211CuO which is close to the binary eutectic of BaCuO2-CuO, and the optimum concentration of the growth system is that wherein the ratio of YBCO to 7BaCuO211CuO is 64:36. The use of a Y2O3-crucible prevents contamination from containers during growth, and facilitates the synthesis of high-purity crystals. Temperature gradient and seed crystals are both effective for controlling nucleation. The annealed crystals show a sharp superconductive transition at 91 K. The temperature dependence of the resistivities is found to be metallic in the ab- as well as the c-direction. Sufficient diamagnetism is manifested as a sharp transition at Tc and a complete shielding effect below Tc.