Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS & MATERIALS  

DOI： 10.2320/matertrans.MF201603

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We present a method for determining the number of stacked layers in graphene by exploiting its light-shielding effect. If a substrate supporting graphene has Raman-active modes, its Raman bands can be obtained simultaneously with the G and G' bands of graphene. The Raman intensities from the substrate decrease with increasing the number of graphene layers because of the low opacity of graphene for visible light. The relationship between the number of graphene layers n and the relative intensities I-n,I-h/I-0,I-h from the substrate can be represented by I-n,I-h/I-0,I-h = 0.977(2n), on the basis of the optical transmittance of visible light for single-layer graphene. The method is simple, convenient, highly accurate, and can be used to count beyond six layers up to 30 layers. (C) 2015 AIP Publishing LLC.

DOI： 10.1063/1.4937140

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS & MATERIALS  

The electronic states of Heusler(L2(1))-type off. stoichiometric Fe2-xV1+xAl have been investigated by soft X-ray angle-resolved photoelectron spectroscopy (ARPES) in order to clarify the origin of their large thermoelectric powers, which cannot be explained in terms of the rigid band model. In off-normal and normal ARPES, Fe2.05V0.95Al shows a weakly dispersive bulk band around the binding energy of 0.3 eV in the Gamma-X direction and an almost dispersion-less one around 0.3 eV in a gap of dispersive bulk bands in the Gamma-L direction, which is attributed to the anti-site Fe defect. At the Gamma point, the bulk band does not appear to cross the Fermi level E-F, consistent with the rigid band model for the excess Fe content bringing about the increase in the valence electrons, but no band crossing E-F down is found at the X point. The anti-site Fe defect states near E-F might push up the band at the X point and cause the p-type thermoelectric properties, unexpected with the rigid band picture. The change in the electronic structures and thermoelectric properties are discussed on the off-stoichiometry and substitution of the forth element.

DOI： 10.2320/jinstmet.JA201517

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The crystal structure and electrical resistivity of YBa2Cu4O8 (Y124) were studied under high pressure up to 18 GPa using diamond-anvil cells, respectively, in order to clarify its conduction mechanism. Y124 causes the first-order phase-transition into the orthorhombic Immm at pressure around 11 GPa. The high-pressure phase (HPP) also shows the superconductivity, while the manner of temperature dependence of electrical resistance and the pressure dependence of transition temperature, T-c, drastically change above 11 GPa. The CuO2 plane persists in HPP but the CuO double chains collapse with the phase transition and transform into three-dimensional Cu-O network, resulting in the renewal of conduction system.

DOI： 10.7566/JPSJ.83.093601

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

We performed x-ray diffraction study and electrical resistivity measurement of non-stoichiometric n-type Bi35Te65 under high pressure to investigate pressure-induced superconductivity and structural phase transition. Stoichiometric bismuth telluride (Bi2Te3), which is a p-type semiconductor, has the rhombohedral structure with space group R-3m at ambient condition. Pressure-induced superconductivity of stoichiometric p-type Bi2Te3 occurs in the high-pressure phases which appear above 8 GPa. Bi35Te65 has also the R-3m structure at ambient condition with electron carriers. X-ray diffraction study shows that the R-3m structure remains stable up to 8 GPa at room temperature. The superconducting transition in n-type Bi35Te65 is observed above 6 GPa; the transition temperature is 2.9 K at 6 GPa. The electrical resistivity at room temperature decreases rapidly at pressures from 7 to 8 GPa, indicating the occurrence of structural phase transition. It suggests that the superconducting transition at 6 GPa occurs at the ambient pressure phase with the R-3m structure.

DOI： 10.1088/1742-6596/500/19/192003

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Measurements of electrical resistivity rho, magnetization M and specific heat C have revealed that SrPt2Sb2 is a type-II superconducting material with a superconducting critical temperature (T-c) of 2.1 K. The electronic specific heat coefficient gamma and the ratio Delta C(T-c)/gamma(T-c )are 9.2(1) mJ mol(-1) K-2 and 1.29, respectively. The temperature dependence of rho exhibits anomalies around 270 K. Synchrotron x-ray diffraction patterns at 295 and 134 K clearly indicate that SrPt2Sb2 undergoes a structural phase transition in the temperature range from 134 to 295 K, suggesting that the anomalies observed in rho around 270 K are related to a structural phase transition.

DOI： 10.1088/0953-2048/26/7/075001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

DOI： 10.7566/JPSJ.82.045002

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Electrical resistivity and x-ray diffraction measurements have been carried out to investigate the pressure effect on the critical temperature for superconductivity (TC) and lattice parameters of AlB2-type superconducting silicide YbGa1.1Si0.9 (TC = 2.4 K) and its reference material CaGaSi (TC = 4.5 K). The electrical resistivity measurements up to 2.5 GPa reveal that TC decreases with pressure for both silicides and the pressure derivative of TC (dTC/dP) is -0.78 K/GPa and -0.026 K/GPa for YbGa 1.1Si0.9 and CaGaSi, respectively. X-ray diffraction measurements up to 3.5 GPa indicate both silicides do not exhibit structural changes in this pressure range and they have similar values for the bulk moduli: B0=40±2 GPa for YbGa1.1Si0.9 and B 0=42±1 GPa for CaGaSi. The relative pressure derivative of TC (dlnTC/dP) and logarithmic volume derivative of T C (dlnTC/dlnV) are -0.33 GPa-1 and 13 in YbGa1.1Si0.9. These values are about tenfold larger than those for other AlB2-type superconductors. Additionally, the origin of dlnTC/dP and dlnTC/dlnV in YbGa1.1Si 0.9 relative to the pressure effect on the valence of Yb atoms is discussed. © 2011 American Physical Society.

DOI： 10.1103/PhysRevB.84.104520

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER PHYSICAL SOC  

Electrical resistivity and x-ray diffraction measurements have been carried out to investigate the pressure effect on the critical temperature for superconductivity (T-C) and lattice parameters ofAlB(2)-type superconducting silicide YbGa1.1Si0.9 (T-C = 2.4 K) and its referencematerial CaGaSi (T-C = 4.5 K). The electrical resistivity measurements up to 2.5 GPa reveal that T-C decreases with pressure for both silicides and the pressure derivative of T-C (dT(C)/dP) is -0.78 K/GPa and -0.026 K/GPa for YbGa1.1Si0.9 and CaGaSi, respectively. X-ray diffraction measurements up to 3.5 GPa indicate both silicides do not exhibit structural changes in this pressure range and they have similar values for the bulk moduli: B-0 = 40 +/- 2 GPa for YbGa1.1Si0.9 and B-0 = 42 +/- 1 GPa for CaGaSi. The relative pressure derivative of T-C (dlnT(C)/dP) and logarithmic volume derivative of T-C (dlnT(C)/dlnV) are -0.33 GPa(-1) and 13 in YbGa1.1Si0.9. These values are about tenfold larger than those for other AlB2-type superconductors. Additionally, the origin of dlnT(C)/dP and dlnT(C)/dlnV in YbGa1.1Si0.9 relative to the pressure effect on the valence of Yb atoms is discussed.

DOI： 10.1103/PhysRevB.84.104520

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To elucidate competition between the Fe-based superconductivity and the antiferromagnetic order of Eu2+, the electrical resistivity of Eu0.85Ca0.15Fe2As2 under high pressure is presented. Under ambient pressure, the Fe-based spin-density-wave (SDW) transition and the antiferromagnetic ordering (AFM) of Eu2+ are observed at T-SDW = 190 K and T-N = 17 K, respectively. With applying pressure, the Fe-based superconductivity with T-c similar to 25 K appears above 1.5 GPa, accompanying collapse of the SDW transition. Compared with EuFe2As2, T-c is close to T-N, which implies strong competition between the superconductivity and the AFM. This competition would lead to non-zero resistivity at lowest temperature.

DOI： 10.1143/JPSJS.80SA.SA117

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The pressure-induced phase transition of bismuth telluride, Bi2Te3, has been studied by synchrotron x-ray diffraction measurements at room temperature using a diamond-anvil cell (DAC) with loading pressures up to 29.8 GPa. We found a high-pressure body-centered cubic (bcc) phase in Bi2Te3 at 25.2 GPa, which is denoted as phase IV, and this phase appears above 14.5 GPa. Upon releasing the pressure from 29.8 GPa, the diffraction pattern changes with pressure hysteresis. The original rhombohedral phase is recovered at 2.43 GPa. The bcc structure can explain the phase IV peaks. We assumed that the structural model of phase IV is analogous to a substitutional binary alloy; the Bi and Te atoms are distributed in the bcc-lattice sites with space group Im (3) over bar m. The results of a Rietveld analysis based on this model agree well with both the experimental data and calculated results. Therefore, the structure of phase IV in Bi2Te3 can be explained by a solid solution with a bcc lattice in the Bi-Te (60 atomic % tellurium) binary system.

DOI： 10.1103/PhysRevB.83.092102

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To clarify competition between FeAs-based superconductivity and antiferromagnetism of Eu2+, and the superconducting properties in EuFe2As2, we investigated a Ca-substituted sample, Eu0.5Ca0.5Fe2As2, under high pressure. Under ambient pressure, the sample exhibits a spin-density-wave (SDW) transition at T-SDW = 191K and antiferromagnetic order at T-N = 4K, but no evidence of superconductivity down to 2K. The Ca-substitution certainly weakens the antiferromagnetism. With increasing pressure, T-SDW shifts to lower temperature and becomes more unclear. Above 1.27 GPa, pressure-induced superconductivity with zero resistivity is observed at around T-c 20K. At 2.14 GPa, T-c reaches a maximum value of 24K and the superconducting transition becomes sharpest. The chemical pressure and the suppression of Eu magnetic order induced by Ca substitution enlarge the zero resistivity region compared to pure EuFe2As2.

DOI： 10.1143/JPSJ.79.073704

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：CERAMIC SOC JAPAN-NIPPON SERAMIKKUSU KYOKAI  

We succeeded in synthesizing Ba2RBiO6 (R = La, Ce, Nd, Sm, Eu, Gd, and Dy) with a double-perovskite structure. Its photocatalytic activities were then investigated for a degradation of methylene blue (MB) solution and gaseous 2-propanol (IPA). High photocatalytic activities were observed under visible light irradiation and also a rare earth dependence of photocatalytic activities in the IPA degradation. We carried out first-principle calculations of the band structure based on the all-electron Full-potential Linear Augmented Plane-Wave (FLAPW) method and discuss the relationship between the high photocatalytic activities and the band structure in this paper. (C) 2010 The Ceramic Society of Japan. All rights reserved.

DOI： 10.2109/jcersj2.118.91

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A single-crystalline sample of BaFe2As2 was prepared by high-pressure synthesis, and temperature dependence of resistivity was measured under high pressures of up to 9.0 GPa. Application of 3.0 GPa pressure suppresses the spin-density wave transition and induces superconductivity with the zero resistance state at a superconducting transition temperature T-c=35 K. T-c decreases monotonically with increasing pressure. The appearance of the superconductivity and the disappearance of the anomaly due to the spin-density wave transition occur simultaneously at a pressure of 3.0 GPa. At 3.0 GPa, a superconducting transition is induced in BaFe2As2; however, the superconductivity is suppressed at higher pressure.

DOI： 10.1103/PhysRevB.79.172506

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The superconductivity of Pr2Ba4Cu7O15-delta (Pr247) is realized at the CuO doublechains. The oxygen deficiency d dependence of the superconducting transition temperature T-c shows the bell-like curve with the maximum of T-c = 20.6 K at delta = 0.64. We investigated the pressure effects on the double-chain superconductivity of Pr247. The resistivity was measured under the pressure of 10 GPa produced by a modified Bridgman anvil type cell. With increasing pressure above 3 GPa, the superconductivity was suppressed and disappeared. The temperature dependence of the resistivity shows a semiconductor like behavior above 5 GPa. The x-ray diffraction using a diamond anvil cell under hydrostatic condition shows that no structural transition occurs below 10 GPa.

DOI： 10.1088/1742-6596/150/5/052079

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Effect of boron on the electric and thermoelectric properties of SrTiO3 has been studied. Boron-doped SrTiO3 was prepared by vacuum annealing of SrTiO3 single crystals in presence of boron vapors. The crystals show low resistivity similar to 0.1 Omega.cm and high Seebeck coefficient of several hundreds mu V/K at a room temperature. It was estimated that almost every boron atom incorporated in SrTiO3 crystal provided a charge carrier. Temperature dependence of Seebeck coefficient and figure of merit ZT were measured as a function of carrier concentration.

DOI： 10.1088/1742-6596/176/1/012042

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATL INST MATERIALS SCIENCE  

We present studies of the thermal, magnetic, and electrical transport properties of reduced polycrystalline Pr2Ba4Cu7O15-delta (Pr247) showing a superconducting transition at T-c = 10-16 K, and compare them with those of as-sintered non-superconducting Pr247. The electrical resistivity in the normal state exhibited T-2 dependence up to approximately 150 K. A clear specific heat anomaly was observed at Tc for Pr247 reduced in a vacuum for 24 h, proving the bulk nature of the superconducting state. By the reduction treatment, the magnetic ordering temperature T-N of Pr moments decreased from 16 to 11 K, and the entropy associated with the ordering increased, while the effective paramagnetic moments obtained from the DC magnetic susceptibility varied from 2.72 to 3.13 mu(B). The sign of Hall coefficient changed from positive to negative with decreasing temperature in the normal state of a superconducting Pr247, while that of the as-sintered one was positive down to 5 K. The electrical resistivity under high magnetic fields was found to exhibit T-alpha dependence (alpha = 0.08-0.4) at low temperatures. A possibility of superconductivity in the so-called CuO double chains is discussed. (c) 2007 Published by Elsevier Ltd.

DOI： 10.1016/j.stam.2007.07.003

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Pressure effects on the Pr2Ba4Cu7O15-delta (Pr247) double chain superconductor was investigated. Its resistivity was measured under a pressure of 8 GPa produced by the modified Bridgman anvil type cell. The magnetic susceptibility measurements up to 1 GPa suggested that the T-c increased and the volume fraction of superconductivity decreased with increasing pressure. In the resistivity measurement, zero resistivityw as not observed above 1 GPa. Moreover, semiconducting behavior was observed at all temperatures at 8 GPa. These results suggest that the superconductivity of Pr247 is suppressed and disappears due to the application of high pressure. The present modified Bridgman anvil type cell is expected to produce a pressure of 10 GPa by the application of a load of 22 tons.

DOI： 10.1143/JPSJS.76SA.92

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We investigated the pressure dependence of the superconducting transition temperature T-c of the MoSr2YCu2O8-delta compound (Mo1212). Superconducting Mo1212 samples were synthesized by a solid-state reaction with multiple annealing processes. T-c-onset of Mo1212 occurred at approximately 40 K at ambient pressure. The pressure dependence of T-c was obtained as 3.3 K/GPa at least up to 8.7 GPa.

DOI： 10.1143/JPSJS.76SA.120

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Structural transformations of MnAs and MnAs0.9Sb0.1 were investigated by X-ray diffraction in high magnetic fields up to 5 T. The temperature dependence of the magnetization was measured in a magnetic field of 0.01 T and the Curie temperature T-C was determined to be 315 K for MnAs and 290 K for MnAs0.9Sb0.1 during heating process. For both compounds, a metarnagnetic transition from a paramagnetic to a ferromagnetic state was observed above T-C. The X-ray diffraction profile at 319 K for MnAs showed a single phase of an orthorhombic MnP-type structure in zero field. An applied magnetic field of 3 T induced the appearance of a hexagonal NiAs-type structure. On further increase of the magnetic field, a single phase with a hexagonal structure was realized above 3.5 T in a forcedferromagnetic state. The X-ray diffraction profile at 295 K for MnAs0.9Sb0.1 showed a hexagonal NiAs-type structure. The coexistence of ferromagnetic and paramagnetic states with different lattice parameters was confirmed in a magnetic field of 2.5 T. The volume expansion induced by a magnetic field was found to be 2.1 % for MnAs and 1.1 % for MnAs0.9Sb0.1.

DOI： 10.1143/JPSJ.75.084604

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In this paper, we review our recent results on magnetic refrigerants MnAs1-xSbx and MnFeAs0.5P0.5 by powder X-ray diffraction measurements in fields up to 5 T and in the temperature range from 8 to 320 K. MnAs shows a first-ordered structural transition with the volume expansion of 2.1% accompanied by a metamagnetic transition, but MnAs0.9Sb0.1 exhibits an isostructural transition with the volume expansion of 1.1%. The cell volume of MnFeAs0.5P0.5 slightly (-0.4%) and continuously decreases with increasing a magnetic field through the metamagnetic transition.

DOI： 10.3233/JAE-2006-734

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Cs2CuBr4 is an S = 1/2 quasi-two-dimensional frustrated antiferromagnet with a distorted triangular lattice parallel to the bc-plane. Cs2CuBr4 undergoes magnetic ordering at T-N = 1.4 K at zero magnetic field. In the ordered phase below T-N, spins lie in a plane that is almost parallel to the bc-plane and form a helical incommensurate structure with ordering vector q(0) = (0, 0.575, 0). The incommensurate spin structure arises from the spin frustration on the distorted triangular lattice. The magnetization curve has a plateau at approximately one-third of the saturation magnetization for magnetic field H parallel to the b- and c-axes, while no plateau is observed for H parallel to a. The ordering vector q(0) increases with increasing magnetic field parallel to the c-axis, and is locked at q(0) similar or equal to (0, 2/3, 0) in the plateau region, which indicates that the up-up-down spin structure is realized in the plateau state. The magnetization plateau should be attributed to quantum fluctuation. For H parallel to b and H parallel to c, the second anomaly suggestive of tiny plateau is observed at roughly two-third of the saturation magnetization. The magnetic field versus temperature diagram is presented. Small amount of Cl- substitution for Br- produces drastic suppression of T-N. With increasing Cl- concentration x, the magnetic ordering disappears at x similar or equal to 0.17. It is also observed that in Cs2Cu(Br1-xClx)(4) phase transition smears with increasing external field and disappears, irrespective of field direction. This should be attributed to the random field effect.

DOI： 10.1143/JPSJS.74S.135

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The structural phase transition induced by magnetic fields on MnAs was observed by the X-ray diffraction measurements in high magnetic fields up to 4 T. Magnetization measurements showed that Curie temperature T-C was 315.5 K for increasing temperatures and a metamagnetic transition from the paramagnetic to the ferromagnetic state occurred above T-C. The structural transformation from the hexagonal NiAs-type to the orthorhombic MnP-type structure was confirmed at T-C with increasing temperature from 290 to 319 K via two-phase coexistence region. The X-ray diffraction profiles at 319 K showed the single phase of the MnP-type structure in zero field and applying magnetic field of 3 T caused appearance of the Brag peak of the hexagonal structure. On further increase of magnetic fields, the single phase of the hexagonal structure was observed above 3.5 T in the forced ferromagnetic state. Both the magnetic and structural transitions induced by magnetic fields above T-C were first order with a hysteresis and had a close relationship between each other. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2004.01.116

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Institute of Metals (JIM)  

Structural transformation induced by magnetic fields on MnAs and MnAs 0.9Sb0.1 was investigated by the X-ray diffraction measurements in high magnetic fields up to 5T. The X-ray diffraction profiles at 319 K for MnAs showed a single phase of the orthorhombic MnP-type structure in zero field, and applying a magnetic field of 3 T caused an appearance of the hexagonal NiAs-type structure. On further increase of magnetic fields, the single phase with the hexagonal structure was confirmed above 3.5 T in a forced ferromagnetic state. The X-ray diffraction profiles at 295 K for MnAs 0.9Sb0.1 showed the hexagonal NiAs-type structure. However, the coexistence of two kinds of the NiAs-type structure with different lattice parameters was confirmed in the magnetic field of 2.5 T. The two phase coexistence was also confirmed in the temperature variation measurements in zero magnetic field. The lattice volume of the ferromagnetic phase was 1.1% larger than that of the paramagnetic phase. These results imply that the transition at TC for MnAs0.9Sb0.1 is of the first-order.

DOI： 10.2320/matertrans.45.311

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The magnetic and structural influences of hydrogen absorption were studied on the itinerant electron metamagnet YCo2. The system YCo2Hx forms two crystalline hydrides of the alpha phase (0<x<0.3) and the beta phase (1.5<xless than or equal to3.5). The hydride samples also include small amounts of the non-intrinsic ferromagnefic component due to the partial structural disordering upon hydrogen absorption. The high field susceptibility indicated that the alpha phase is an itinerant electron metamagnet in which the critical field is possibly lower than that of YCo2. The beta phase has no metamagnetic transition. The hydrogen-induced changes in the magnetic properties are discussed on the basis of the itinerant electron magnetism. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/S0925-8388(03)00110-5

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The magnetization of Ce2Fe17 was precisely measured under high pressures up to 1.2 GPa in magnetic fields up to 18 T. The magnetic phase diagram in the B-T plane is determined at 0, 0.3, 0.4, 0.6, 0.9 and 1.2 GPa. At 0 GPa, five magnetic phases exist and the application of high pressure produces two additional magnetic phases. The shape of the phase diagram changes drastically with increasing pressure. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(02)02511-5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：INST PURE APPLIED PHYSICS  

The magnetic field effects on the thermodynamic properties of chemical reactions were systematically studied. In the formulation. the chemical influence of magnetic fields due to magnetostatic energy was represented by the magneto-chemical potential for each component and the magnetic free energy change per unit reaction. Then the general formulae were derived for the magnetic field-induced changes in the equilibrium constant and the Beat, free energy and entropy of reaction. In the calculation, the general formulae were applied to a ferromagnetic metal-hydrogen reaction and the magnetic field effects were numerically evaluated for two reactions in the single system LaCo5-H-2. In the experiment, the magnetic field effects were observed by applying high magnetic fields of 10-30T to the system LaCo5-H-2. The observed results agreed qualitatively and quantitatively with the corresponding calculated ones. This study resolved the issue of the thermodynamic effects of magnetic fields on chemical reactions.

DOI： 10.1143/JJAP.41.416

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We experimentally investigated the effects of magnetic fields on the heat of reaction by examining the metal-hydrogen system LaCo5-H-2. The heat of reaction was measured in zero field and a magnetic field by the logarithmic pressure vs. inverse temperature method and the calorimetric one. Both the methods gave generally the same results that the magnetic field caused the absolute value of the heat of reaction to increase a little in the alpha + beta region and decrease considerably in the beta + gamma region. These agree well with the calculation based on the general formulation of magneto-thermodynamic effects in chemical reactions. This is the first observation of the magnetic field effect on the heat of reaction. (C) 2002 Elsevier Science B.V. All rights reserved.

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The equilibrium hydrogen pressures in the beta(1) + gamma region of the ferromagnetic hydride PrCo5Hlambda have been investigated as a function of the hydrogen composition x under the influence of magnetic fields up to 5 T at 273.2 K. The logarithmic pressure change is increased linearly with increasing magnetic fields and depends on the hydrogen composition. The value DeltaM(s) (die change in saturation magnetization per desorbed molH) is calculated from the relationship between the pressure change and the magnetic field. The results show a peculiar dependence of the DeltaM(s) on the hydrogen composition. The maximum value of DeltaM(s) of 25 J T-1 molH(-1) at x=4.3 is much larger than that observed in other metal-hydrogen systems. (C) 2002 Published by Elsevier Science B.V.

DOI： 10.1016/S0925-8388(01)01646-2

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The effects of magnetic fields were generally formulated on the thermodynamic properties of chemical reactions. The magnetic M C field-induced change in the heat of reaction was calculated for the metal-hydrogen system, especially for LaCo5-H-2, on the basis of the general formulation. Independently of this, the heat of reaction under the influence of magnetic fields was estimated from the temperature dependence of the equilibrium hydrogen pressure. The agreement between both the results indicated that magnetic fields influence the heat of reaction in metal-hydrogen systems. (C) 2002 Elsevier Science BY All rights reserved.

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Electronic structures of the pseudo-binary compound Y(Co, Ni)(5) with the CaCu5-type hexagonal structure are calculated in the self-consistent linear muffin-tin orbital method within the atomic sphere approximation, by taking into account the preferential occupation sites for Ni. The calculated bulk moment disappears abruptly near 60% Ni concentration. Above the critical concentration of Ni, a metamagnetic transition from the paramagnetic to the ferromagnetic state is found to occur. These calculated results are consistent with the recently observed ones. It has been shown that the anomalous magnetic behaviours of Y(Co, Ni)(5) can be explained by the detailed shape of the local density-of-states curve of the 3d-transition-metal atoms at the 3g site near the Fermi level.

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We studied the magnetoresistance of Ni/Al-Al2O3/Co tunnel junctions at T > 1.4 K. Below the superconducting transition temperature of deposited Al films, a nonmonotonic magnetoresistance was observed. The fractional change in junction resistance was 14% at 1.4 K. The nonmonotonic behavior of the magnetoresistance can be explained in terms of the dependences of the superconducting energy gap and the sheet conductivity of the Al layer on the magnetic field. This explanation was supported by the results of an experiment on an Al-Al2O3/Ni tunnel junction which also showed a large magnetoresistance below T-c due to the superconductivity effect.

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The gel-melting temperature was observed for aqueous agarose and aqueous methyl cellulose gels which were prepared under the influence of magnetic fields up to 5 T. The exposure to magnetic fields during gelation caused the melting temperature to increase in the agarose gels (+1.0K for the 0.2 wt% gel) and to decrease in methyl cellulose gels (-3.5 K for the 0.4 wt% gel). The change in melting temperature was reduced with increasing polymer concentration and was saturated in magnetic fields below 3 T. Stable gel structures were constructed due to the exposure to magnetic fields.

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Itinerant electron metamagnetism was studied by ultra-high field magnetization for the system Y(CO1-xNix)(3) (x = 0 similar to 0.1). The metamagnetic transition fields were observed to increase with increasing the number of 3d electrons. This is attributed to the decrease in the exchange field acting on the 3d moment.

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The magnetization of the metal hydrides GdFe3Hx (x=0 similar to 3.6) and Dy6Fe23Hx (x=0 similar to 20.3) was measured in magnetic fields up to 29 T at 77 K. For these measurements the hydrides were prepared in situ in a glass holder with gradually varying hydride composition x at room temperature. For each system the magnetization curve varied systematically with hydrogen content. The dependence of magnetization on hydrogen content is discussed.

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A general thermodynamic theory was constructed on magnetic field effects on chemical equilibria. Introducing the magnetochemical potential or the electromagnetic chemical potential leads to the magnetic field-induced changes in the equilibrium constant in an ideal gas reaction and the electromotive force in an electrochemical system. Applying these general results to metal-hydrogen systems gives the relationships between the equilibrium hydrogen pressure or the equilibrium electrode potential and magnetic fields, which correspond to experimental data.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The magnetic field-induced shift in chemical equilibrium was studied for the ferromagnetic hydride LaCo5Hx-hydrogen system. The hydrogen composition x, which was monitored via the magnetization of the hydride, was observed as a function of magnetic fields up to 14 T under a constant pressure of hydrogen at 313.2 K. The hydrogen composition is gradually changed by 50% from x = 1.88 to x = 0.96 as the applied magnetic field was changed from 2 to 14 T. A thermodynamic theory can explain this effect, taking the change in magnetic free energy into account.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA LAUSANNE  

Electrical resistivity of the unstable metal hydrides LaNi5Hx and LaCo5Hx has been measured in situ by a newly developed method where the samples are under the influence of mechanical stress. An activated sample does not give the bulk resistivity of the hydride, but the resistivity change with hydrogen pressure or temperature is correlated with the transformation of hydride phases. The resistivity of the bulk hydride is tolerably obtained in the first absorption of hydrogen for a virgin sample. The resistivity at 323 K is 1.3, 15.3 and 8.5 mu Omega m for the metal phase (x = 0), the alpha phase (x similar or equal to 0.6) and the beta phase (x = 6.7) of LaNi5Hx, and 1.5, 11.5 and 18.8 mu Omega m for the metal phase (x = 0), the beta phase (x = 3.4) and the gamma phase (x = 4.3) of LaCo5Hx, respectively. These resistivity changes with hydrogen composition are interpreted in relation to disordered-ordered arrangement of hydrogen.

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