Kiyokazu Nozawa

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.

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.

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.

Magnetic Properties of Phenyl Nitronyl Nitroxides

Abstract Magnetic properties and crystal structures of several derivatives of phenyl nitronyl nitroxide (abbreviated as PNN; 2-phenyl-4,4,5,5-tetramethyl-4,5-dihydro-lH-imidazol-l-oxyl-3-N-oxide) are investigated. Some of them have the intermolecular interactions between the nitroxide group and the phenyl group, which are suggested to be favorable to ferromagnetic coupling. As a result of the coexistence of different types of magnetic interactions, anomalies in the temperature dependence of paramagnetic susceptibility are found for some compounds.

Magnetic properties and crystal structures of 2-hydro and 2-halo nitronyl nitroxide radical crystals

Abstract Magnetic properties and crystal structures of 2-hydro, 2-bromo and 2-iodo nitronyl nitroxide radicals (abbreviated as HNN, BrNN and INN, respectively), [HNN = 2-hydro-4,4,5,5,-tetramethyl 4,5-dihydro-1H-imidazol-1-oxyl 3-oxide], were investigated. These three radical crystals have similar structural units. In particular, BrNN and INN have almost the same molecular packings. However, only INN exhibits dominant ferromagnetic interactions.

Organic radical crystals, α-nitronyl nitroxide family: High-field magnetization study

Abstract Studies of intermolecular antiferromagnetic interactions in the crystals of several derivatives of α -nitronyl nitroxide radical by magnetization (up to 400 kOe) and susceptibility (1.8–300 K) measurements are presented. The estimated exchange couplings are attributed to the specific molecular arrangements, by making reference to the crystal structures.

Electrical Conductivity of Nickel Phosphides

Five nickel phosphides, Ni2P, NiP, NiP2, NiP2 (high pressure form) and NiP3 which have interesting crystal structures have been prepared at high temperatures and high pressures. The electrical resistivity, dc magnetic susceptibility and photoelectron spectrum of nickel phosphides have been studied. Five nickel phosphides show the metallic behavior though their crystal structures and Ni–Ni distances are remarkably different. The relationship between the crystal structures and physical properties of the nickel phosphides is discussed.

The cation radical salts of the oxygen-substituted donor, bedo-TTF

Abstract The electrocrystallization of BEDO-TTF using the supporting electrolytes containing CuCl 2 , HgCl 2 , HgBr 2 , HgI 2 , Hg(SCN) 2 , ReO 4 , SbF 6 , and HCTNN anions gave conducting ion radical salts. Except the ‘CuBr 2 ’ salt, these newly prepared materials exhibit metallic conductivities. The HCTMM salt (from Ph-CN) showed two dimensional conducting behavior which is consistent with the crystal structure.

Magnetic Interactions in the Crystals of α- and β-Phases of 2-Hydro Nitronyl Nitroxide and Related Compounds

Abstract Magnetic properties and crystal structures of α-and β-2-hydro nitronyl nitroxide radicals (2-hydro-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl 3-oxide) were investigated. Exchange couplings in both phases were estimated from the parainagnetic susceptibility (1.8-300 K) and magnetization (up to 400 kOc) measurements. Assignment of the couplings to molecular packings has been carried out. Close spacing between the ONCNO moietics yields various magnitude of exchange couplings from 0 to ca.-30 K. In α-phase crystal, short contacts between the central carbon atoms with negative spin density and the NO groups with positive spin density were observed. However, this packing is assigned to an antiferromagnetic exchange coupling, J/kB = −11 K (ℋ= −2JS 1.S 2). This case suggests that care must be taken when we refer to McConnells proposal.

Superconductivity of ZrRuP

Hexagonal ZrRuP, HfRuP and Hf0.5Zr0.5RuP and orthorhombic ZrRuP which show an interesting superconductivity have been prepared at high temperatures and high pressures. The electrical resistivity and the dc magnetic susceptibility of these phosphides have been studied at low temperatures. The superconducting transition temperatures of the phosphides with the hexagonal structure were much higher than those with the orthorhombic structure.