Electric dipole induced bulk ferromagnetism in dimer Mott molecular compounds.

Magnetic properties of Mott-Hubbard systems are generally dominated by strong antiferromagnetic interactions produced by the Coulomb repulsion of electrons. Although theoretical possibility of a ferromagnetic ground state has been suggested by Nagaoka and Penn as single-hole doping in a Mott insulator, experimental realization has not been reported more than half century. We report the first experimental possibility of such ferromagnetism in a molecular Mott insulator with an extremely light and homogeneous hole-doping in π-electron layers induced by net polarization of counterions. A series of Ni(dmit)2 anion radical salts with organic cations, where dmit is 1,3-dithiole-2-thione-4,5-dithiolate can form bi-layer structure with polarized cation layers. Heat capacity, magnetization, and ESR measurements substantiated the formation of a bulk ferromagnetic state around 1.0 K with quite soft magnetization versus magnetic field (M-H) characteristics in (Et-4BrT)[Ni(dmit)2]2 where Et-4BrT is ethyl-4-bromothiazolium. The variation of the magnitude of net polarizations by using the difference of counter cations revealed the systematic change of the ground state from antiferromagnetic one to ferromagnetic one. We also report emergence of metallic states through further doping and applying external pressures for this doping induced ferromagnetic state. The realization of ferromagnetic state in Nagaoka-Penn mechanism can paves a way for designing new molecules-based ferromagnets in future.

Magnetic Fe@FeOx, Fe@C and α-Fe2O3 Single-Crystal Nanoblends Synthesized by Femtosecond Laser Ablation of Fe in Acetone.

There are few reports on zero-field-cooled (ZFC) magnetization measurements for Fe@FeOx or FeOx particles synthesized by laser ablation in liquids (LAL) of Fe, and the minimum blocking temperature (TB) of 120 K reported so far is still much higher than those of their counterparts synthesized by chemical methods. In this work, the minimum blocking temperature was lowered to 52 K for 4⁻5 nm α-Fe2O3 particles synthesized by femtosecond laser ablation of Fe in acetone. The effective magnetic anisotropy energy density (Keff) is calculated to be 2.7⁻5.4 × 105 J/m³, further extending the Keff values for smaller hematite particles synthesized by different methods. Large amorphous-Fe@α-Fe2O3 and amorphous-Fe@C particles of 10⁻100 nm in diameter display a soft magnetic behavior with saturation magnetization (Ms) and coercivities (Hc) values of 72.5 emu/g and 160 Oe at 5 K and 61.9 emu/g and 70 Oe at 300 K, respectively, which mainly stem from the magnetism of amorphous Fe cores. Generally, the nanoparticles obtained by LAL are either amorphous or polycrystalline, seldom in a single-crystalline state. This work also demonstrates the possibility of synthesizing single-crystalline α-Fe2O3 hematite crystals of several nanometers with (104), (113), (116) or (214) crystallographic orientations, which were produced simultaneously with other products including carbon encapsulated amorphous Fe (a-Fe@C) and Fe@FeOx core-shell particles by LAL in one step. Finally, the formation mechanisms for these nanomaterials are proposed and the key factors in series events of LAL are discussed.

Fungus-derived hydroxyl radicals kill hepatic cells by enhancing nuclear transglutaminase.

We previously reported the importance of induced nuclear transglutaminase (TG) 2 activity, which results in hepatic cell death, in ethanol-induced liver injury. Here, we show that co-incubation of either human hepatic cells or mouse primary hepatocytes derived from wild-type but not TG2-/- mice with pathogenic fungi Candida albicans and C. glabrata, but not baker's yeast Saccharomyces cerevisiae, induced cell death in host cells by enhancing cellular, particularly nuclear, TG activity. Further pharmacological and genetic approaches demonstrated that this phenomenon was mediated partly by the production of reactive oxygen species (ROS) such as hydroxyl radicals, as detected by a fluorescent probe and electron spin resonance. A ROS scavenger, N-acetyl cysteine, blocked enhanced TG activity primarily in the nuclei and inhibited cell death. In contrast, deletion of C. glabrata nox-1, which encodes a ROS-generating enzyme, resulted in a strain that failed to induce the same phenomena. A similar induction of hepatic ROS and TG activities was observed in C. albicans-infected mice. An antioxidant corn peptide fraction inhibited these phenomena in hepatic cells. These results address the impact of ROS-generating pathogens in inducing nuclear TG2-related liver injuries, which provides novel therapeutic targets for preventing and curing alcoholic liver disease.

Direct observation of collective modes coupled to molecular orbital-driven charge transfer.

Correlated electron systems can undergo ultrafast photoinduced phase transitions involving concerted transformations of electronic and lattice structure. Understanding these phenomena requires identifying the key structural modes that couple to the electronic states. We report the ultrafast photoresponse of the molecular crystal Me4P[Pt(dmit)2]2, which exhibits a photoinduced charge transfer similar to transitions between thermally accessible states, and demonstrate how femtosecond electron diffraction can be applied to directly observe the associated molecular motions. Even for such a complex system, the key large-amplitude modes can be identified by eye and involve a dimer expansion and a librational mode. The dynamics are consistent with the time-resolved optical study, revealing how the electronic, molecular, and lattice structures together facilitate ultrafast switching of the state.

Bilayer mott system with cation···anion supramolecular interactions based on a nickel dithiolene anion radical: coexistence of ferro- and antiferromagnetic anion layers and large negative magnetoresistance.

A novel bilayer Mott system, (Et-4BrT)[Ni(dmit)2]2 (Et-4BrT = ethyl-4-bromothiazolium; dmit = 1,3-dithiole-2-thione-4,5-dithiolate), contains two nonequivalent Ni(dmit)2 anion layers, where both layers form Mott insulating states. Supramolecular Br(cation)···S(anion) and S(cation)···S(anion) interactions play a crucial role in constructing the bilayer structure. The ferro- and antiferromagnetic short-range-ordering layers coexist in the crystal, which achieves large negative magnetoresistance (Δρ/ρ0 ≈ -75% at 70 kOe) at 5 K under 1 GPa.

Bilayer Mott system based on Ni(dmit)2 (dmit = 1,3-dithiole-2-thione-4,5-dithiolate) anion radicals: two isostructural salts exhibit contrasting magnetic behavior.

A new class of Ni(dmit)(2) anion radical salt (Et-2,5-DBrP)[Ni(dmit)(2)](2) (1) (Et-2,5-DBrP = ethyl-2,5-dibromopyridinium) was developed. Single-crystal X-ray diffraction analysis indicates that this salt contains two crystallographically independent anion layers in the crystal with effective Br···S halogen bonds between the cation and the anion. The crystal and electronic structures, and electrical and magnetic measurements reveal that 1 is a novel bilayer Mott system, in which two different Mott-insulating anion layers coexist in one crystal. Selective halogen substitution of Br with I at the 2-position in the cation affords the isostructural bilayer salt (Et-2I-5BrP)[Ni(dmit)(2)](2) (2) (Et-2I-5BrP = ethyl-2-iodo-5-bromopyridinium), while substitution at the 5-position results in a structural change, yielding the monolayer salt (Et-2Br-5IP)[Ni(dmit)(2)](2) (3) (Et-2Br-5IP = ethyl-2-bromo-5-iodopyridinium). These results indicate that the halogen bond plays an important role to realize the bilayer system, and that the crystal structure is controlled by tuning the strength of the halogen bond. The low temperature magnetic properties of the two isostructural salts 1 and 2 are significantly different, because they are affected by fluctuated spins that do not participate in the formation of short-range antiferromagnetic domains. The bilayer salt generates the fluctuated spins more easily than conventional monolayer salts, and such fluctuated spins are expected to result in unique physical properties.

Heat capacity reveals the physics of a frustrated spin tube.

We report on theoretical and experimental results concerning the low-temperature specific heat of the frustrated spin-tube material [(CuCl(2)tachH(3)Cl]Cl(2) (tach denotes 1,3,5-triaminocyclohexane). This substance turns out to be an unusually perfect spin-tube system which allows to study the physics of quasi-one-dimensional antiferromagnetic structures in rather general terms. An analysis of the specific-heat data demonstrates that at low enough temperatures the system exhibits a Tomonaga-Luttinger liquid behavior corresponding to an effective spin-3/2 antiferromagnetic Heisenberg chain with short-range exchange interactions. On the other hand, around 2 K the composite spin structure of the chain is revealed through a Schottky-type peak in the specific heat. We argue that the dominating contribution to the peak originates from gapped magnon-type excitations related to the internal degrees of freedom of the rung spins.

Transport mechanisms in metallic and semiconducting single-wall carbon nanotube networks.

A fundamental understanding of the conduction mechanisms in single-wall carbon nanotube (SWCNT) networks is crucial for their use in thin-film transistors and conducting films. However, the uncontrollable mixture state of metallic and semiconducting SWCNTs has always been an obstacle in this regard. In the present study, we revealed that the conduction mechanisms in nanotube networks formed by high-purity metallic and semiconducting SWCNTs are completely different. Quantum transport was observed in macroscopic networks of pure metallic SWCNTs. However, for semiconducting SWCNT networks, Coulomb-gap-type conduction was observed, due to Coulomb interactions between localized electrons. Crossovers among a weakly localized state and strongly localized states with and without Coulomb interactions were observed for transport electrons by varying the relative content of metallic and semiconducting SWCNTs. It was found that hopping barriers, which always exist in normal SWCNT networks and are serious obstacles to achieving high conductivity, were not present in pure metallic SWCNT networks.

Intrinsic magnetoresistance of single-walled carbon nanotubes probed by a noncontact method.

The intrinsic magnetotransport effect of the single-walled carbon nanotube (SWNT) has been observed by the cavity perturbation technique, which is a noncontact method for evaluating transport properties. The inverse Q factor of the cavity resonator, which corresponds to the resistance of the sample, shows a linear increase as a function of the magnetic field. The angular and tube diameter dependence of oriented SWNT thin films, and measurements using sorted SWNTs reveal that the observed positive magnetoresistance is due to the Aharonov-Bohm effect of metallic nanotubes.

Magneto-optical studies of low-dimensional organic conductors.

Our periodic orbit resonance (POR) results on quasi-two-dimensional (q2D), highly anisotropic q2D and quasi-one-dimensional (q1D) organic conductors are reviewed together with our rotational cavity magneto-optical measurement system. Higher order POR up to seventh order has been observed in the q2D system (BEDT-TTF)2Br(DIA), and the experimental conditions to observe POR and the cyclotron resonance (CR) are discussed. Highly anisotropic q2D Fermi surface (FS) in ß″-(BEDT-TTF)(TCNQ), which was considered to have q1D FS previously, is proposed by our POR measurements, and the possible interpretations of other experimental results of ß″-(BEDT-TTF)(TCNQ) are discussed assuming the highly anisotropic q2D FS. Finally, detailed q1D FS of (DMET)2I3, obtained from our POR results, is discussed in connection with the typical q1D system (TMTSF)2ClO4.

Hybrid molecular material exhibiting single-molecule magnet behavior and molecular conductivity.

Two unique materials based on Mn4 single-molecule magnet (SMM) clusters (ST=9) and integer or non-integer average valent platinum maleonitriledithiolate (mnt2-) complexes, [{MnII2MnIII2(hmp)6(MeCN)2}{Pt(mnt)2}2][Pt(mnt)2]2.2MeCN (1) and [{MnII2MnIII2(hmp)6(MeCN)2}{Pt(mnt)2}4][Pt(mnt)2]2 (2), were synthesized by the material diffusion method and electrochemical oxidation, respectively (hmp-=2-hydroxymethylpyridinate). 1 and 2 are comprised of four and six [Pt(mnt)2]n- units, respectively, in addition to a common MnII2MnIII2 double-cuboidal unit, [MnII2MnIII2(hmp)6(MeCN)2]4+ (hereinafter [Mn4]4+). Among the [Pt(mnt)2]n- units, two units in 1 and four units in 2 are coordinated with the [Mn4]4+ unit, forming a 1D chain of {-[Mn4]-[Pt(mnt)2]2-} for 1 and a discrete subunit of {[Pt(mnt)2]2-[Mn4]-[Pt(mnt)2]2} for 2. The other two [Pt(mnt)2]n- units, occupying void space of the packing, form a stacking column with the coordinating [Pt(mnt)2]n- units, finally constructing hybrid frames of aggregates consisting of [Mn4]4+ units and [Pt(mnt)2]n- units. Electronic conductivity measurements revealed that 1 is an insulator and 2 is a semiconductor with sigma=0.22 S.cm(-1) at room temperature and an activation energy of 136 meV. Detailed magnetic measurements proved that the [Mn4]4+ units in 1 and 2 behave as SMMs with an ST=9 ground state at low temperatures. There is no significant interaction between [Mn4]4+ units and [Pt(mnt)2]n- units, but interactions between localized spins of [Pt(mnt)2]n- were detected even in 2 at low temperatures where the conductivity is electronically insulated. 2 is the first example of a hybridized material exhibiting SMM behavior and electronic conductivity.