田島 裕之

We have developed a technique to measure the thermal conductivity, which enables us to measure for organic samples over a wide temperature range between 4 K and room temperature. In our technique, two heaters and three thermometers are installed unlike the conventional one-heater-two-thermometer configuration. We describe the detailed design of our cell and the procedure for measurements. We have succeeded in measuring the thermal transport of organic molecular crystals with the conductivity of the order of similar to 1 W/K m, by employing our method. (C) 2005 American Institute of Physics.

An organic semiconductor (BEDT-TTF)Cu 2Br 4 exhibits rather high conductivity (10 -2 S/cm with little sample dependence) despite the fact that BEDT-TTF molecules have a divalent closed-shell state as evidenced by ESR and Raman measurements. In order to obtain insight into the properties of the charge carriers, the Hall coefficient for the semiconductor was measured in the temperature range of 120-300 K. Charge carriers are electronlike and their concentration is rather low [(4±2) × 10 19/mol at room temperature]. The carrier concentration increases exponentially with temperature with an activation energy of 0.17 eV below 170 K and 0.12 eV above 170 K. The Hall mobility is as high as 2 cm 2/Vs, supporting the high conductivity of the material. Thermo-electric power measurements also support the sign and concentration of the charge carriers. The carrier concentration at room temperature is one order of magnitude lower than the concentration of Curie spin due to the presence of π electrons at low temperatures. The fine structure of the ESR signal from the Curie spin shows smearing above 100 K. This behavior is caused by exchange interaction mediated via conduction electrons. These results indicate that charge carriers localized at low temperatures are thermally activated to the conduction band at high temperatures. The possible origins of the charge carriers are discussed in terms of impurity sites of the different crystal phases of (BEDT-TTF) 2[Cu 4Br 6(BEDT-TTF)] in the matrix. ©2005 The American Physical Society.

An organic semiconductor (BEDT-TTF)Cu2Br4 exhibits rather high conductivity (10(-2) S/Cm with little sample dependence) despite the fact that BEDT-TTF molecules have a divalent closed-shell state as evidenced by ESR and Raman measurements. In order to obtain insight into the properties of the charge carriers, the Hall coefficient for the semiconductor was measured in the temperature range of 120-300 K. Charge carriers are electronlike and their concentration is rather low [(4 +/- 2) X 10(19) /mol at room temperature]. The carrier concentration increases exponentially with temperature with an activation energy of 0.17 eV below 170 K and 0.12 eV above 170 K. The Hall mobility is as high as 2 cm(2)/Vs, supporting the high conductivity of the material. Thermo-electric power measurements also support the sign and concentration of the charge carriers. The carrier concentration at room temperature is one order of magnitude lower than the concentration of Curie spin due to the presence of pi electrons at low temperatures. The fine structure of the ESR signal from the Curie spin shows smearing above 100 K. This behavior is caused by exchange interaction mediated via conduction electrons. These results indicate that charge carriers localized at low temperatures are thermally activated to the conduction band at high temperatures. The possible origins of the charge carriers are discussed in terms of impurity sites of the different crystal phases of (BEDT-TTF)(2)[Cu4Br6(BEDT-TTF)] in the matrix.

We have grown high-quality beta-FeSi2 single crystals by the temperature gradient solution growth (TGSG) method using Fe2Si5 solute and Zn solvent. The grown crystals were polyhedral and typical size was (2-4) x (1-3) x (1-2) mm(3) for the growth period of 336 h. The FWHM of the X-ray rocking curve at beta-FeSi2 800 diffraction was 63 arcsec. Hall measurements revealed that the crystals showed a p-type conductivity. The hole concentration and Hall mobility at room temperature were (2-3) x 10(17) cm(-3) and 20-50 cm(2)/Vs, respectively. We also measured the solubility of Fe2Si5 solute in Zn solvent. The solubility was about 2wt% at 880 degrees C, which is about two times higher than that of FeSi2 in Zn solvent. (C) 2004 Elsevier B. V. All rights reserved.

We have measured the thermal conductivity of organic molecular crystals (DMe-DCNQI)2 Li1-x Cux (0≤x≤0.14) over a wide temperature range between 4 and 250 K. We observed the phonon contribution in the whole range measured. A phonon peak was observed near ∼20 K. This peak denotes a crossover between the phonon mean free path that diverges as T-2 and the phonon specific heat that decreases as T3. The peak height decreases with the reduction of Cu concentration x and vanishes in the x=0 sample. We discuss this behavior in terms of the spin-Peierls local lattice distortion. © 2005 The American Physical Society.

Some new findings concerning the structural, optical, transport and magnetotransport properties of τ-(EDO-S,S-pMEDT-TTF)2(AuBr 2)1+y and τ-(P-S,S-DMEDT-TTF)2(AuBr 2)1+y (y ≈ 0.75) are reported. Some similarities and dissimilarities in the properties are discussed. The dissimilarities are more pronounced at low temperatures and high magnetic fields. The results are compared to those obtained of other conducting multilayered systems.

Pc-based conductors with clearly defined structures were evaluated. When planar Pc complexes were the components, only the 1D system was obtained. However, these complexes were found to exhibit properties as a 1D system. Furthermore, it was observed that the electronic properties at low temperature were severely affected by the defects or impurities in the crystal due to their highly one-dimensional electronic structure. These results provide evidence that most of the M(Pc)Xy one-dimensional partially oxidized salts do not show metal-to-insulator transitions with definite lattice distortions down to very low temperature.

The transmission measurements were performed to investigate the optical absorption spectra near the fundamental absorption edge of β-FeSi 2 single crystals. In the low temperature absorption spectra region, the phonon structure corresponding to the emission and absorption components was observed. A phonon energy of 0.031±0.004 eV was found by assuming the exciton state in the indirect allowed transition. The results show a value of 0.814 eV for the exciton transition energy at 4 K.

We present the infrared and Raman spectra of β″-(BEDT-TTF) 3(ReO4)2 (BEDT-TTF=bis-ethylenedithio- tetrathiafulvalene) measured at various temperatures. We investigated the three C=C stretching modes, ν2ν27, and ν3. The infrared and Raman spectra discontinuously changed at 80 K. Below 80 K, for example, the doublet ν2 bands split into three peaks, the doublet ν27 also split into three, and a mutual exclusion rule for the vibronic ν3 modes in the infrared and Raman spectra was broken. This symmetry lowering was consistent with the result of x-ray crystal structure analyses conducted at 100 K and 22 K. The site charges in the unit cell estimated from the splitting of ν2 were +0.73,+0.7 3, and +0.53 in the metallic phase, and they were +0.2, +0.85, and +0.95 in the insulating phase. The metal-insulator transition of this compound was characterized as the charge-ordering transition originated from the localization of charge due to Coulomb interactions.

We have prepared organic thin films of soluble dicyano(phthalocyaninato)iron salt, [(n-C7H15)(4)N][Fe-III(Pc)(CN)(2)], and fabricated the electroluminescence (EL) devices having the Metal-Insulator-Metal structure. The device exhibits emission for both positive and negative bias voltages. We observed two bands in the EL spectra. One band was assigned to the Q band of the phthalocyanine molecule. The other, which shifts with changing the applied voltage, could correspond to the metal-to-ligand charge transfer (MLCT) band and/or the ligand-to-metal charge transfer (LMCT) band.

We present the infrared and Raman spectra of beta"-(BEDT-TTF)(3)(ReO4)(2) (BEDT-TTF=bis-ethylenedithio-tetrathiafulvalene) measured at various temperatures. We investigated the three C=C stretching modes, nu(2),nu(27), and nu(3). The infrared and Raman spectra discontinuously changed at 80 K. Below 80 K, for example, the doublet nu(2) bands split into three peaks, the doublet nu(27) also split into three, and a mutual exclusion rule for the vibronic nu(3) modes in the infrared and Raman spectra was broken. This symmetry lowering was consistent with the result of x-ray crystal structure analyses conducted at 100 K and 22 K. The site charges in the unit cell estimated from the splitting of nu(2) were +0.7(3),+0.7(3), and +0.5(3) in the metallic phase, and they were +0.2,+0.8(5), and +0.9(5) in the insulating phase. The metal-insulator transition of this compound was characterized as the charge-ordering transition originated from the localization of charge due to Coulomb interactions.

We studied the optical absorption, polarized reflectance (PR) and photoluminescence (PL) of β-FeSi2 single crystals grown from solution. In low-absorption measurements, we found a phonon emission and absorption structure, which suggests an indirect transition. The exciton energy gap of 0.814 eV was determined from the absorption spectrum at 3.5 K. We also found a direct transition with the gap energy of 0.939 eV. PR measurements for E//a, E//b and E//c revealed the anisotropy of reflectivity of β-FeSi 2. We observed the PL with a peak wavelength of about 1.56 μm at 20 K. © 2004 Elsevier B.V. All rights reserved.

We synthesized TPP[FeIII(Pc)(CN)2]2, PTMAx[FeIII(Pc)(CN)2]·y(MeCN), and PXX [FeIII(Pc)(CN)2], a new series of charge-transfer salts containing the axially-substituted phthalocyanine (Pc), [Fe III(Pc)(CN)2]-. In this molecular unit, the π conduction electron derived from the Pc-ring coexists with the d electron which is a potential source of a local magnetic moment. Therefore various phenomena associated with the interplay between local magnetic moments and conduction electrons are expected. We observed the giant negative magnetoresistance (GNMR) in all the three salts. The GNMR is highly anisotropic for the magnetic-field direction, and reflects the g-tensor anisotropy of the local magnetic moment in the [FeIII(Pc)(CN)2]- unit. This indicates that the GNMR in these salts originates from the strong π-d interaction in the [FeIII(Pc)(CN)2]- unit. © 2004 Elsevier Ltd. All rights reserved.

We obtained three conducting crystals based on a [Fe-III(Pc)(CN)(2)] molecular unit. All crystals showed a large anisotropic negative magnetoresistance arising from the pi-d interaction self-contained in the [Fe-III(Pc)(CN)(2)] unit. The anisotropy is attributable to the anisotropic g-tensor in the [Fe-III(Pc)(CN)(2)] unit. We also obtained a thin film containing [Fe-III(Pc)(CN)(2)]. The film exhibits photocurrent response for the UV irradiation. These features suggest [M(Pc)(CN)(2)] molecular unit is a well-designed one for a building block of molecular devices.

We report Raman and infrared spectra at room and low temperature on single crystals of β-(ET)2PF6, which exhibits a metal-insulator (M-I) transition at 297 K (=TM−I). Both spectra exhibit drastic changes below TM−I. By analyzing the C=C stretching mode (υ2) appearing in the Raman spectra, we conclude that the charges on ET molecules are disproportionate below TM−I and evaluate the charge densities on ET molecules. The infrared conductivity spectra demonstrate that the fluctuation of the charge order survives still in the metallic phase above TM−I. On the basis of a mean-field approximation, we calculate the infrared conductivity spectra in the insulating phase of this salt. The calculated spectra are consistent with those experimentally obtained. © 2004 The American Physical Society.

Cu L2,3-edge X-ray absorption spectra for (Me 2-DCNQI)2Li1-xCux alloys (Me 2-DCNQI: 2,5-dimethyl-N,N′-dicyanoquinonediimine) were measured in order to investigate the local electronic structure around Cu atoms. Both in the Cu L3- and L2-edge regions, (Me 2-DCNQI)2Cu (x=1) shows a characteristic band higher in energy than the lowest sharp band associated with the transitions to the Cu 3d hole; on the other hand, K3Cu(CN)4 with Cu 3d 10 configuration shows only the higher-energy band. These higher-energy bands arise from the transitions to the lowest unoccupied molecular orbitals of Me2-DCNQI and CN ligand molecules, respectively, where the intensity comes from the Cu 3d components through strong hybridization between metal and ligand. The spectral feature does not change even if the x value is reduced to less than 0.1, indicating that the alloys have nearly the same covalent bond between Cu and Me2-DCNQI as (Me2-DCNQI)2Cu (x=1), independent of the substitution. This demonstrates that we can control the filling and the dimensionality of electronic structure in Me2-DCNQI charge-transfer complexes through the replacement of Li by Cu. © 2003 Elsevier B.V. All rights reserved.

A novel phthalocyanine conductor containing 2-D &pi;&ndash;&pi; stacks of the partially oxidized Co(Pc)(CN)₂ units has been obtained by the electrochemical oxidation method with PXX. The crystal is highly conductive (>10³ S cm^&minus;1) at all the temperatures measured (5 K < T < 300 K). Though the metallic character becomes clearer compared with the single chain or ladder chain conductors, the 2-D sheet has been found to be still anisotropic.

The polarized optical reflectance spectra of the quasi-two-dimensional organic correlated electron system κ (BEDT TTF)2 Cu[N(CN)2]Y, Y = Br and Cl are measured in the infrared region. The former shows the superconductivity at Tc≃11.6K and the latter does the antiferromagnetic insulator transition at TN≃28K. Both the specific molecular vibration mode ν3(ag) of the BEDT-TTF molecule and the optical conductivity hump in the mid-infrared region change correlatively at T*≃38K of κ (BEDT TTF)2Cu[N(CN)2]Br, although no indication of T* but the insulating behavior below Tins≃50−60K are found in κ − (BEDT − TTF)2Cu[N(CN)2]Cl. The results suggest that the electron-molecular vibration coupling on the ν3(ag) mode becomes weak due to the enhancement of the itinerant nature of the carriers on the dimer of the BEDT-TTF molecules below T*, while it does strong below Tins because of the localized carriers on the dimer. These changes are in agreement with the reduction and the enhancement of the mid-infrared conductivity hump below T* and Tins, respectively, which originates from the transitions between the upper and lower Mott-Hubbard bands. The present observations demonstrate that two different metallic states of κ − (BEDT − TTF)2Cu[N(CN)2]Br are regarded as a correlated good metal below T* including the superconducting state and a half filling bad metal above T*. In contrast the insulating state of κ − (BEDT − TTF)2Cu[N(CN)2]Cl below Tins is the Mott insulator. © 2004 The American Physical Society.

The polarized optical reflectance spectra of the quasi-two-dimensional organic correlated electron system κ-(BEDT-TTF)2Cu[N(CN) 2]Y, Y=Br and Cl are measured in the infrared region. The former shows the superconductivity at Tc≃11.6 K and the latter does the antiferromagnetic insulator transition at TN≃28 K. Both the specific molecular vibration mode v3(ag) of the BEDT-TTF molecule and the optical conductivity hump in the mid-infrared region change correlatively at T*≃38 K of κ-(BEDT-TTF) 2Cu[N(CN)2]Br, although no indication of T* but the insulating behavior below Tins≃50-60 K are found in κ-(BEDT-TTF)2Cu[N(CN)2]Cl. The results suggest that the electron-molecular vibration coupling on the v3(ag) mode becomes weak due to the enhancement of the itinerant nature of the carriers on the dimer of the BEDT-TTF molecules below T*, while it does strong below Tins because of the localized carriers on the dimer. These changes are in agreement with the reduction and the enhancement of the mid-infrared conductivity hump below T* and Tins, respectively, which originates from the transitions between the upper and lower Mott-Hubbard bands. The present observations demonstrate that two different metallic states of κ-(BEDT-TTF)2Cu[N(CN)2]Br are regarded as a correlated good metal below T* including the superconducting state and a half filling bad metal above T*. In contrast the insulating state of κ-(BEDT-TTF)2Cu[N(CN)2]Cl below Tins is the Mott insulator.

Refractive index of β-FeSi2has been investigated by polarized optical reflection measurement on a bulk β-FeSi2single crystal and Kramers-Kronig analysis. Anisotropy of refractive index was clearly observed for the light polarization of E//a, E//b and E//c. ©2004 IEEE.

Solid state properties of dicyano(2,3-naphthalocyaninato)cobalt(III) neutral radical crystal, [Co(2,3-Nc)(CN)(2)]CH3CN, were characterized by measurements of the resistivity under high pressure and under uniaxial strain, thermoelectric power, magnetic susceptibility, ESR and polarized reflectance spectra. The title compound exhibited thermally activated-type electrical conductivity along the c-axis. The room temperature (RT) resistivity rho(RT) along the c-axis and activation energy E-a rapidly decreased with increasing pressure. The temperature-dependent thermoelectric power S was that of a typical one-dimensional (ID) semiconductor. However the high absolute value of S suggested that this electronic system should be strongly correlated. Although the electrical resistivity exhibited monotonous temperature-dependence, the magnetic susceptibility clearly indicated a Peierls-type transition and marked fluctuation from RT. Both Peierls-type transitions and fluctuations are characteristic phenomena to 1D conductors. Furthermore ESR spectra manifested that the Peierls-type transition occurred at 100 K. The inconsistency between the electrical behavior (without a phase-transition) and magnetic behavior (with a phase-transition) indicates separation of the degrees of freedom in spin and charge (spin-charge separation) of this material. Spin-charge separation is a theoretically predicted phenomenon peculiar to the ID conductors with strong correlation. The reflectance spectra were quantitatively explained by a 1D Hubbard model, and manifested the existence of a structural fluctuation of this material from RT. Based on these observed physical properties it is concluded that [Co(2,3-Nc)(CN),]CH,CN is a strongly correlated ID semiconductor with a Mott(Hubbard) type energy gap and characterised with a fluctuation and spin-charge separation. Copyright (c) 2004 Society of Porphyrins S Phthalocyanines.

The polarized optical reflectance spectra of κ-(BEDT-TTF) 2Cu(NCS)2 and its deuterated one are measured in the infrared region. Both the specific molecular vibration mode v3(a g) of the BEDT-TTF molecule and the optical conductivity hump in the mid-infrared region change correlatively at T*=45-50K. The results suggest that the electron-molecular vibration coupling on the v3(a g) mode becomes weak due to the enhancement of the itinerant nature of the carriers on the BEDT-TTF dimers below T*. The present observations demonstrate that two different metallic states are regarded as a correlated good metal below T* and a half filling bad metal above T*. © EDP Sciences.

Some new findings concerning the structural, optical, transport, and magnetotransport properties of τ-phase organic conductors, based on the donor molecules ethylenedioxy-S,S-dimethyletnylenedithio-tetrathiafulvalene, ethylenedioxy-R,R-dimethylethylenedithio-tetrathiafulvalene, pyrazino-S,S-dimethylethylenedithio-tetrathiafulvalene, pyrazino-R,R-dimethylethylenedithio-tetrathiafulvalene, pyrazino-r-dimethylethylenedithio-tetrathiafulvalene, pyrazino-S,S-dimethylethyledithio-diselenadithiafulvalene, pyrazino-Mnethylethylenedithio-tetrathiafulvalene, and pyrazino-r-methylethylenediseleno-tetrathiafulvalene are described. Some similarities and differences in their properties are discussed.

We studied C=C stretching bands of β&quot;-(ET) 3 (ReO 4 ) 2 and β&quot;-(ET) 4 M(CN) 4 H 2 O (M=Pt, Pd and Ni) at the low temperatures below 300 K in order to verify the inhomogeneous charge distributions. A drastic spectral change was observed for β&quot;-(ET) 3 (ReO 4 ) 2 at 80 K, below which the system falls into the charge ordered state. On the other hand, a continuous spectral change was observed for β&quot;-(ET) 4 Ni(CN) 4 H 2 O and β&quot;-(ET) 4 Pd(CN) 4 H 2 O. v 2 for M=Ni and Pd exhibited a doublet, suggesting an inhomogeneous charge distributions. v 2 for M=Pt did not show a peak splitting, while C=C bands for the deuterium analogue exhibited a behaviour similar to those for M=Ni. © EDP Sciences.

We measured the static magnetic susceptibility and the electron spin resonance of the Fe(Pc)(CN)_2 complexes, and investigated the molecular magnetism of the unit Fe(Pc)(CN)_2. The magnetic susceptibility shows a highly anisotropic Curie behavior. Based on the electron spin resonance, we found a highly anisotropic g-value (g_1 = 3.62, g_2 = 1.11, and g_3 =0.52) in the molecular unit Fe(Pc)(CN)_2. This anisotropy is caused by the molecular orbital angular momentum in the degenerate next highest occupied molecular orbitals of the molecular unit Fe(Pc)(CN)_2. Since the molecular unit Fe(Pc)(CN)_2 has a unique structure with fourfold symmetry, the molecular orbital angular momentum has a finite value of l_z 〜 +1 and -1. The anisotropic molecular magnetism of the unit Fe(Pc)(CN)_2 contributes the highly anisotropic Curie behavior. The molecular unit Fe(Pc)(CN)_2 is a good candidate for a molecular magnet having high magnetic anisotropy.

The Fermi surface (FS) shape of the organic superconductor (MDT-TSF)(AuI2)(0.436) with an incommensurate anion structure (MDT-TSF: methylenedithio-tetraselenafulvalene) has been investigated by means of the optical reflectance spectra and angular-dependent magnetoresistance oscillations (AMRO). The difference of the plasma frequencies between the interstack and the intrastack directions indicates that the overall band structure has small anisotropy (omega(p,perpendicular to)/omega(p,parallel to) approximate to 0.62). The observation of the AMRO shows the presence of a small closed orbit, which can be assigned to the overlapped area of the large FS. This demonstrates that the incommensurate anion potential is crucial to remove the degeneracy of the energy bands on the zone boundary. The magnetoresistance peak in the fields applied within the conducting layers shows an unusually large interlayer transfer integral (t(perpendicular to) approximate to 1 meV) among organic superconductors.

We measured optical reflectance, Raman spectra, magnetic susceptibility, and electron paramagnetic resonance for the molecular conductor (IEDT)[Pd(dmit)_2]. The excitation from the bonding molecular orbital to the antibonding orbital in the Pd(dmit)_2 dimer causes a strtking peak in the optical spectra around 11000 cm^<-1>. By analyzing the spectral intensity for this peak, we determined the degree of the charge transfer from the IEDT molecule to the Pd(dmit)_2 molecule. A gap structure appears below 2000 ^<-1> in the reflectance spectra below 100 K. The magnetic susceptibility decreases around 100 K. These phenomena suggest a reduction in the density of states The electron paramagnetic resonance measurement reveals that the g_<b-> value decreases around 80K. This is due to a reduction in the paramagnetic contribution of the Pd(dmit)_2 layer. The Ag modes of the Pd(dmit)_2 molecule become infrared-active below 100 K as a result of the broken symmetry in the Pd(dmit)_2 layer. We propose that the resistance anomaly around 80 K originates from the charge density wave formation within the Pd(dmit)_2 layer.

NiO nanoparticles were produced by annealing Ni(OH)(2) monolayer-nanoclusters above 973 K in air. Their diameters were estimated to be between 2 and 6 nm from X-ray diffraction patterns. In the magnetization measurements superparamagnetic or ferromagnetic behaviors were observed and characteristic properties of NiO nanoparticles were confirmed. (C) 2003 Elsevier Science B.V. All rights reserved.

We have fabricated a light-emitting diode from horse-heart cytochrome c and measured the electro-luminescence (EL) spectra. The spectra exhibit broad peaks around 530 and 690 nm, and a weak shoulder around 410 nm. The EL spectra are completely different from the photo-luminescence spectra previously reported. The appearance of the 690 nm emission band suggests the charge-transfer between the iron and the axial methionine ligand plays a crucial role in the electrical conduction in the cytochrome c film. (C) 2003 Elsevier Science Ltd. All rights reserved.

A τ-type organic conductor, τ-(P-S,S-DMEDT-TTF) 2(AuBr2)1+y, (y∼0.75) shows large negative magnetoresistance (ΔAR/R ∼ -0.9) and Shubnikov-de Haas (SdH) oscillations originated from small Fermi pockets at low temperature in the apparent semiconducting state. Polarized reflectance spectra were measured to elucidate the effect of the magnetic filed on the low temperature electronic state. Temperature dependence of the spectra shows at least four kinds of temperature regions divided at 11, 40 and 100 K, respectively. It was succeeded to observe the relatively large recovery of spectral intensity especially below 1500 cm-1 by the application of the magnetic field along the c-axis (Faraday configuration), while the magnetic field gives minor effect on the spectral shape in the energy range in this study. © 2003 Elsevier Science B.V. All rights reserved.

We measured the polarized reflectance and Raman spectra of β-(BEDT-TTF)2PF6 from 360 K down to 5 K. Both the IR and Raman spectra show the drastic changes below 280 K at which the metal-insulator transition occurs. On lowering the temperature, the Raman band at 1470 cm-1 shows a split suggesting the charge disproportionation (CD) among BEDT-TTF molecules. © 2003 Elsevier Science B.V. All rights reserved.

We have studied the magnetic susceptibility for one-dimensional system, TPP[FeIIIxCoIII1-x(Pc)(CN) 2]2 (0.07 ≤ x ≤ 1). At x = 1, the system shows anisotropic Curie-Weiss behavior and spontaneous magnetization below 6 K. The temperature below which spontaneous magnetization occurs (Tc) shifts downward with adecrease in FeIII concentration, but is still above 2 Kat x = 0.07. The anisotropic Curie-Weiss behavior in the susceptibility was observed for all the alloys measured. This magnetic anisotropy was associated with the g-tensor anisotropy in the [FeIII(Pc)(CN)2] unit. © 2003 Elsevier Science B.V. All rights reserved.

The magnetic torque shows the anomaly around 20K. The torque curve suggests the antiferromagnetic state in the one-dimensional Fe(Pc)(CN)(2) chain. The magnetic easy axis is directed along the CN-ligand in the Fe(Pc)(CN)(2) unit. Because of the strong spin-orbit coupling, the next highest occupied molecular orbital is also ordered so that the molecular orbital angular momentum of the neighboring Fe(Pc)(CN)(2) unit is antiparallel. We observed the weak ferromagnetism below 6K. This is ascribed to the canting of the antiparallel moments.

The infrared reflectance spectra of α-ET2KHg(SCN)4 in applied magnetic fields up to 9.8 T are reported. A dip structure appears in the reflectance spectra around 1000 cm-1 below 10 K at B = 0 T. This structure is associated with the density-wave formation in this salt. Under a magnetic field above 4 T, this dip structure disappears. A phase transition at a low magnetic field less than 4 T is suggested. © 2002 Elsevier Science B.V. All rights reserved.

We have measured the angular dependence of the ESR spectra on DMDP[FeIII0.01CoIII0.99(Pc)(CN) 2] (DMDP = dimethyldiphenylphosphonium, Pc = phthalocyanine), which is the alloy system of magnetic FeIII and non-magnetic CoIII. The spectra exhibit giant anisotropic shift in g-value of iron(III). We also report the temperature dependence of the polarized reflectance spectra of one-dimensional conductors, TPP[FeIII(Pc)(CN)2]2 and TPP[CoIII(Pc)(CN)2]2 (TPP = tetraphenylphosphonium). With lowering the temperature, the plasma edge drastically shifts to a higher wavenumber in both salts. © 2002 Elsevier Science B.V. All rights reserved.

We measured the electron spin resonance and the magnetoresistance in the iron(III) phthalocyanine complexes. The electron spin resonance in PNP[Fe(Pc)(CN)2] reveals the large anisotropy of the g-value. This is due to the strong spin-orbit coupling in the second HOMO (the third HOMO) hybridizing the dyz (dzx) orbital in the central Fe atom. This anisotropic g-value is consistent with the anisotropy of the magnetic susceptibility and the negative magnetoresistance in TPP[Fe(Pc)(CN)2]2. We also measured the large negative magnetoresistance in [PXX][Fe(Pc)(CN)2] and (PTMA)x[Fe(Pc)(CN)2]Y(CH3CN). The iron(III) phthalocyanine complexes are the good materials for the research of the one-dimensional π-d electron system. © 2002 Elsevier Science B.V. All rights reserved.

We measured thermoelectric power and Raman spectra for (Me(2)DCNQI)(2)CuxLi1-x. The v(8) (quinoid C=N stretch) Raman line shifts downwards with an increase of copper contents (x), and exhibits a split for x less than or equal to 0.24. Temperature dependence of the thermoelectric power exhibits drastic change between x = 0.14 and x = 0.22. This behaviour is consistent with the phase diagram previously determined. (C) 2002 Elsevier Science B.V. All rights reserved.

We fabricated thin films from an acetone solution containing [(n-C₇H₁₅)₄N]₂[Fe^II(Pc)(CN)₂] (Pc = phthalocyanine). The quality of films was improved by the pretreatment of the substrate with 3-trimethoxysilylpropyl chloride. The fabricated films exhibit the photoswitching phenomenon for ultraviolet (UV) irradiation.

Low-temperature crystal structure and optical properties of the quasi-one-dimensional organic conductor (ChTM-TTP)_2GaCl_4 (ChTM-TTP : 2-[4,5-(1,2-cyclohexylenedithio)-1,3 -dithiol-2-ylidene]-5-[4,5-bis(methylthio)-1,3-dithiol-2-ylidene]-1,3,4,6-tetrathiapentalene) have been investigated. As the temperature lowers,the disordered anion transforms to an ordered state with a superstructure wave vector of q = (2/1, 0, 2/1). The peak intensities of the superlattice gradually increase in the metallic region,and are saturated below 150 K; this indicates that the charge localization below 150 K is independent of the evolution of the superlattice. The reflectance spectra of (ChTM-TTP)_2X suggest the existence of moderate interchain interactions. The transverse interactions are more pronounced in the GaCl_4 salt(t⊥/t_‖&ap;1/7) than the AuBr_2 and Au(CN)_2 salts. The low-temperature optical reflectance of the GaCl_4 salt shows no significant change, indicating that (ChTM-TTP)_2GaCl_4 goes to an insulating state with a small charge gap, which is consistent with the transport property. The low-frequency peak in the chainaxis optical conductivity is attributed to a correlation gap, though the expected on-site Coulomb repulsion U is relatively small.

The magnetoresistance study on TPP[M(Pc)(CN)(2)](2) (M = Fe, Co, Fe0.30CO0.70) salts is reported. These three salts have similar columnar structures, nevertheless exhibit different electrical behaviors. TPP[Fe(Pc)(CN)(2)](2) exhibits anisotropic giant negative magnetoresistance, while TPP[Co(Pc)(CN)(2)] exhibits large positive magnetoresistance. The alloyed compound, TPP[Fe-0.30 Co-0.70 (Pc)(CN)(2)](2), also exhibits anisotropic negative magnetoresistance, although the decrease in the resistivity under the magnetic field is less than that of TPP[Fe(Pc)(CN)(2)](2). The g-tensor anisotropy in the [Fe(Pc)(CN)(2)] unit qualitatively explains the field-orientation dependence of the negative magnetoresistance. Magnetic fluctuation associated with a weak-ferromagnetic transition is suggested as a possible origin of the giant negative magnetoresistance. (C) 2002 Elsevier Science (USA).

Raman spectra of (Me<FONT SIZE="-1">₂</FONT>-DCNQI)<FONT SIZE="-1">₂</FONT>Cu<FONT SIZE="-1">_x</FONT>Li<FONT SIZE="-1">_1-x</FONT> (0&le; x&le; 1) have been measured at room temperature, 200 K, 100 K and 5 K. The observed Raman bands are assigned on the basis of the vibrational analysis done by Lunardi and Pecile. The Raman band assigned to the a<FONT SIZE="-1">_g</FONT>v<FONT SIZE="-1">_R8</FONT> fundamental mode (quinoid C=N stretching) shifts downward with an increase of x and exhibits a remarkable split for 0&le; x&le; 0.29. This frequency shift is attributable to the change of a charge density on a Me<FONT SIZE="-1">₂</FONT>-DCNQI molecule. From the split of the &upsilon;<FONT SIZE="-1">_R8</FONT> Raman band, it is concluded that the charge densities on Me<FONT SIZE="-1">₂</FONT>-DCNQI molecules are not equivalent even at room temperature for 0&le; x&le; 0.29.

Two-dimensional organic τ-type conductors show metallic temperature dependence of resistivity down to Tmin = 30-50 K, below which a resistivity upturn is observed. A large negative magnetoresistance appears below Tmin suddenly in temperature. Below about 4 K, magnetoresistance in any direction is extremely hysteretic in field-, temperature- or field-angle-sweep, and ρ⊥(H//plane) shows switching between two- and four-fold depending on magnetic and thermal history, indicating magnetic domain generation. Static susceptibility shows slight ferromagnetic component. NMR is in favor of anti-ferromagnetism below about 15 K. These two results imply that the system is a weak ferromagnetic one. Preliminary optical reflectance and specific heat studies implied metallic state at low temperature, but no clear-cut proof has been shown whether or not the ground state is metallic. This report presents giant Shubnikov de Haas (SdH) oscillation in both τ-(EDO-S,S-DMEDT-TTF)2(AuBr2)1+y, and τ-(P-S,S-DMEDT-TTF)2(AuBr2)1+y, (y ∼ 0.75), which is a clear evidence for the metallic ground state. However, the observed Fermi surfaces (FS) are 0.65 and 6.1% of the first Brillouin zone for τ-(EDO-S,S-DMEDT-TTF)2(AuBr2)1+y, and 2.3 and 6.9% for τ-(P-S,S-DMEDT-TTF)2(AuBr2)1+y, (y ∼ 0.75), which suggest extremely small FS pockets, and were not expected by the previous band calculation. Further, it is surprising that the Dingle temperature was around 1 K, indicating unexpectedly clean, while residual resistivity ratio is about 1. We note that the fundamental oscillation of 0.65% is already n = 2 state, which is already next to the Landau quantum limit. © 2002 Published by Elsevier Science Ltd.

We study the electronic properties of quasi-one-dimensional V6O13 which exhibits a metal-insulator transition using angle-resolved photoemission spectroscopy (ARPES), optical conductivity, and soft X-ray Raman spectroscopy (SXRS). From ARPES, we observe an energy gap of 0.2eV across the metal-insulator transition with change in the lower Hubbard band. Band dispersion is found only along the b-axis, consistent with highly anisotropic behavior observed in optical conductivity and SXRS measured on the same samples. These results indicate the electronic properties of V6O13 are dominated by b-axis electronic structure. (C) 2002 Elsevier Science B.V. All rights reserved.

A single-sided magneto-optical (MO) disk with a thin substrate was previously studied in a stress-balanced disk in order to prevent disk deformation in a wide temperature and humidity range. We succeeded in the suppression of transitional disk tilt by developing new UV resins. Environment-proof mechanical characteristics to enable mobile use were satisfied for a high-density disk with a thin substrate, In this paper, we report that disk tilt within +/-0.5 mrad (+/-0.03 degree) was achieved in a 0.5-mm-thick and 50-mm-diameter disk.

Temperature dependence of the polarized reflectance spectra have been measured on the single crystals of θ-ET2MM′(SCN)4[MM′=RbCo, RbZn, CsZn] salts. The reflectance spectra of RbCo and RbZ salts exhibit drastic change around 190 K for samples cooled down slowly (dT/dt∼-0.1 K/min). This spectral change disappears for the samples cooled down rapidly (dT/dt∼ - 1 K/min). The reflectance spectra of MM′ = CsZn salt exhibit Drude-like future down to 20 K. Charge-ordering patterns on these salts are deduced by the spectral analysis using mean-field calculations.

With the axially CN-substituted phthalocyanines, novel one-dimensional conductors, (PTMA)x[MIII(Pc)(CN)2] ·yCH3CN (M = Co and Fe) have been obtained. Although their crystal structures appear as if they were simple salts, their physical properties show metallic behaviors. These crystals are therefore partially oxidized salts in which part of the cation sites are replaced by CH 3CN. Especially, when M = Fe, the Pc unit has a local magnetic moment and a 1-D π-d system is formed. The existence of the π-d interaction is suggested from the electrical and magnetic measurements.

The electric resistivity was measured for τ- (EDO-S,S-DMEDT-TTF) 2(AuBr2)1+y (1), τ-(EDO-S,S-DMEDT-TTF) 2- (I3)1+y (2) and τ-(P-S,S-DMEDT-TTF) 2(AuBr2)1+y (3), (y∼0.75) under hydrostatic pressure and magnetic field. Pressure increases the M-I transition temperature of (2) and (3). The period of the angular dependence of the magnetoresistance of (1) at 5 T changes from 90° to 180° by pressure of 5 kbar, while that of (2) and (3) is not changed.

Temperature dependence of the polarized reflectance spectra have been measured on the single crystals of theta-ET2MM&apos; (SCN)(4) [MM&apos; = RbCo, RbZn, CsZn] salts. The reflectance spectra of RbCo and RbZn salts exhibit drastic change around 190 K for samples cooled down slowly (dT/dt similar to -0.1 K/min). This spectral change disappears for the samples cooled down rapidly (dT/dt similar to -1 K/min). The reflectance spectra of MM = CsZn salt exhibit Drude-like future down to 20 K. Charge-ordering patterns on these salts are deduced by the spectral analysis using mean-field calculations.