Yuko Hosokoshi

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.

Ferroelectric Properties and Nano-Scaled Domain Structures in (1-x)BiFeO3-xBaTiO3 (0.33 < x < 0.50)

We have investigated ferroelectric domain structures in the pseudo-cubic structure of (1-x)BiFeO3-xBaTiO3 with 0.33 < x < 0.50 by the transmission electron microscopy (TEM). High-resolution lattice image reveals that the psudo-cubic structures in the x = 0.33, 0.40 and 0.50 compounds are characterized as nano-scaled coexisting state of the polar rhombohedral structure and the non-polar cubic one. Furthermore, P-E hysteresis curve measurements showed that the x = 0.33, 0.40 and 0.50 compounds are regarded as ferroelectric materials with the spontaneous polarizations of 41 μC/cm2, 21 μC/cm2, and 5 μC/cm2, respectively.

Se-Substitution and Cation Effects on the High-Pressure Molecular Superconducior, β-Me4N[Pd(dmit)2]2 -A Unique Two-Band System

Abstract Crystal and electronic structures and physical properties of the molecular conductors Me4Z [Pd(L)2]2 (Z = N, P, As, and Sb; L = dmit and dmise) are described. Every salt has very similar crystal structure with “solid-crossing” columns. The behavior of resistivity under pressure depends on the Se-substitution and the choice of the cation. Tight-binding band calculations indicate that these salts form a unique two-band system. The narrow and two-dimensional HOMO (anti-bonding) band is thought to form the half-filled conduction band. Magnetic properties suggest that the insulating state under ambient pressure comes from the strong electron-electron correlation. The one-dimensional LUMO (bonding) band is located below the HOMO band. The application of pressure induces an overlap of these two bands and changes the band filling, which brings forth the metallic state. The system under higher pressure, however, shows non-metallic behavior probably due to the one-dimensional instability associated with th...

A New Ferrimagnet Based on a Radical-Substituted Radical Cation Salt

Radical-substituted radical cations are attractive spin building blocks of molecule-based magnets. The introduction of an additional spin as a counteranion provides a unique three-spin system wherein the magnetic interactions between the spins of the radical substituent and the radical cation (J(intra)) and those between the spins of the radical cation and the anion (J(inter)) play decisive roles in determining the magnetic properties of the system. We report the first demonstration of a ferrimagnet by utilizing a large-J(intra) system, nitronyl nitroxide-substituted dihydrophenazine radical cation (NNDPP(*+)) in combination with tetrabromoferrate (FeBr(4)(-)) as the counteranion. On the basis of measurements of dc and ac magnetic susceptibilities and heat capacity, the magnetic properties of NNDPP(*+) x FeBr(4)(-) are elucidated to be those of a three-dimensional long-range-ordered ferrimagnet with T(c) = 6.7 K.

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.

Magnetic Properties and Structures of the α- and δ-Phases of p-NPNN

We have investigated the crystal structures and magnetic properties of the α- and δ-phases of an organic radical p -NPNN ( p -nitrophenyl α-nitronyl nitroxide), which yielded the first organic bulk ferromagnet, β- p -NPNN (the β-phase). The results are compared with those of the β- and γ-phases, which show distinct magnetic ordering due to intermolecular ferromagnetic couplings. Common structural features are found in the four phases. Unlike the other phases, the α-phase exhibits a weak antiferromagnetic interaction. This is attributable to phenyl–phenyl overlapping found only in the α-phase. The crystal structure of δ- p -NPNN contains a packing motif similar to that of the γ-phase. Though the δ-phase exhibits ferromagnetic interactions, it shows no magnetic ordering down to 0.46 K. It is suggested that ferromagnetic two-leg spin ladders are formed in the δ-phase, instead of a two-dimensional network as in γ- p -NPNN. This low dimensionality explains the absence of a magnetic transition.

Pressure effect on organic radicals

Abstract The magnetic properties of galvinoxyl (4-[3,5-bis(1,1-dimethylethyl)-4-OXO-2,5-cyclohexadiene-1-ylidenemethyl]-2,6-bis (1,1-dimethyl-ethyl)-phenoxy) and F5PNN (2-pentafluorophenyl-4,4,5,5-tetramethyl-4,5-dihydro-lH-imidazol-1-oxyl 3-oxide) under pressure are presented. We have found that the structural changes of both compounds can be suppressed by pressurization. The phase transition to a diamagnetic state of galvinoxyl can be suppressed by applied pressure. It has been found that under 7 kbar, the transition is sufficiently suppressed and the ferromagnetic interactions are preserved down to low temperature. The temperature dependence of the paramagnetic susceptibility under 7 kbar obeys the ferromagnetic chain model with 2J/kB = 25 K. The room-temperature crystal structure of F5PNN involves a uniform chain, while the low-temperature magnetism can be interpreted by the alternating antiferromagnetic chain model with 2J/K B = -5.6 K and α = 0.4. We found that under 5 kbar, the low-temperature magn...

Low-Temperature Magnetic Properties of Nitronyl Nitroxides

Abstract Magnetic properties of two nitronyl nitroxide (4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazol-1-oxyl 3-oxide) radicals which show nearly isotropic S=½ alternating linear chains are investigated down to 0.5 K and up to 9 T. Pentafluorophenyl nitronyl nitroxide at low temperatures shows an antiferromagnetic chain with alternation, while the material at room temperature shows a uniform chain structure. 2-Methyl nitronyl nitroxide, which contains an alternating chain with ferromagnetic and antiferromagnetic interactions, exhibits a three-dimensional phase transition at 1.3 K.

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.