Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

DOI： 10.7566/jpsj.92.035002

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

DOI： 10.7566/jpsj.92.013701

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

DOI： 10.7566/jpsj.91.113701

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

We discover superconductivity (SC) in LaAgSb2 at ambient pressure and its close correlation with a charge density wave (CDW) under pressure. The superconducting transition temperature (Tc) exhibits a sharp peak at a CDW critical pressure of 3.2 GPa. We demonstrate that the carriers inhabiting the Sb-square net are crucial not only in the formation of CDW but also in SC for their relatively strong electron-phonon coupling (EPC). Furthermore, theoretical EPC strength in pristine LaAgSb2 cannot explain the observed peak with Tc - 1 K, which indicates that an additional mechanism reinforces SC only around the CDW critical pressure.

DOI： 10.1103/PhysRevB.106.L161113

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Oxygen is a unique molecule that possesses a spin quantum number S=1. In the condensed phases of oxygen, the delicate balance between the antiferromagnetic interaction and van der Waals force results in the various phases with different crystal structures. By applying ultrahigh magnetic fields, the antiferromagnetic coupling between O2 molecules breaks, and novel high-field phases can appear. We have investigated the physical properties of condensed oxygen under ultrahigh magnetic fields and have found that the stable crystal structure of solid oxygen changes around 100 T. Even in liquid oxygen, we observed a strong acoustic attenuation, which indicates the fluctuation of local molecular arrangements. These results demonstrate that magnetic fields can modulate the packing structure of oxygen through spin-lattice coupling. Our study implies the possibility of controlling oxygen-related (bio-)chemical processes by using an external magnetic field.

DOI： 10.3390/oxygen2020013

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Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physrevb.105.035108

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Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physrevb.104.224423

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Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

DOI： 10.1103/physrevb.104.l140402

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DOI： 10.1103/physrevb.103.085134

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Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

DOI： 10.7566/jpsj.89.114711

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DOI： 10.1103/physrevresearch.2.043090

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Applied Physics  

We have measured the temperature dependence of resistivity in single-crystalline CeNiGe3 under hydrostatic pressure in order to establish the characteristic pressure-temperature phase diagram. The transition temperature to AFM-I phase T-N1 = 5.5 K at ambient pressure initially increases with increasing pressure and has a maximum at similar to 3.0GPa. Above 2.3 GPa, a clear zero-resistivity is observed (SC-I phase) and this superconducting (SC) state coexists with AFM-I phase. The SC-I phase suddenly disappears at 3.7 GPa simultaneously with the appearance of an additional kink anomaly corresponding to the phase transition to AFM-II phase. The AFM-II phase is continuously suppressed with further increasing pressure and disappears at similar to 6.5 GPa. In the narrow range near the critical pressure, an SC phase reappears (SC-II phase). A large initial slope of upper critical field mu H-0(c2) and non-Fermi liquid behavior indicate that the SC-II phase is mediated by antiferromagnetic fluctuations. On the other hand, the robust coexistence of the SC-I phase and AFM-I phase is unusual on the contrary to superconductivity near a quantum critical point on most of heavy-fermion compounds.

DOI： 10.7566/jpsj.89.063702

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This study investigates the transport properties of a chiral elemental semiconductor tellurium (Te) under magnetic fields and pressure. Application of hydrostatic pressure reduces the resistivity of Te, while its temperature dependence remains semiconducting up to 4 GPa, contrary to recent theoretical and experimental studies. Application of higher pressure causes structural as well as semiconductor-metal transitions. The resulting metallic phase above 4 GPa exhibits superconductivity at 2 K along with a noticeable linear magnetoresistance effect. On the other hand, at ambient pressure, we identified metallic surface states on the as-cleaved (10 (1) over bar0) surfaces of Te. The nature of these metallic surface states has been systematically studied by analyzing quantum oscillations observed in high magnetic fields. We clarify that a well-defined metallic surface state exists not only on chemically etched samples that were previously reported, but also on as-cleaved ones.

DOI： 10.1103/physrevb.101.245111

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Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

DOI： 10.7566/jpsj.89.053701

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Authorship：Last author   Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Journal of the Physical Society of Japan  

DOI： 10.7566/jpscp.30.011030

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Authorship：Last author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society (APS)  

Antiferromagnet Mn3P with Neel temperature T-N = 30 K is composed of Mn tetrahedrons and zigzag chains formed by three inequivalent Mn sites. Due to the nearly frustrated lattice with many short Mn-Mn bonds, competition of the exchange interactions is expected. We here investigate the magnetic structure and physical properties including pressure effect in single crystals of this material, and reveal a complex yet well-ordered helimagnetic structure. The itinerant character of this materials is strong, and the ordered state with small magnetic moments is easily suppressed under pressure, exhibiting a quantum critical point at similar to 1.6 GPa. The remarkable mass renormalization, even in the ordered state, and an incoherent-coherent crossover in the low-temperature region, characterize an unusual electronic state in Mn3P, which is most likely effected by the underlying frustration effect.

DOI： 10.1103/physrevlett.124.087202

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DOI： 10.1103/physrevb.100.214105

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Publishing type：Research paper (scientific journal)   Publisher：Informa UK Limited  

DOI： 10.1080/14786435.2018.1511070

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Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

DOI： 10.7566/jpsj.87.024702

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IEEE  

We here report magnetostriction measurements under pulsed megagauss fields using a high-speed 100 MHz strain monitoring system devised using fiber Bragg grating (FBG) technique with optical filter method. The optical filter method is a detection scheme of the strain of FBG, where the changing Bragg wavelength of the FBG reflection is converted to the intensity of reflected light to enable the 100 MHz measurement. In order to show the usefulness and reliability of the method, we report the measurements for solid oxygen, spin-controlled crystal, and volborthite, a deformed Kagome quantum spin lattice, using static magnetic fields up to 7 T and non-destructive millisecond pulse magnets up to 50 T. Then, we show the application of the method for the magnetostriction measurements of CaV4O9, a two-dimensional antiferromagnet with spin-halves, and LaCoO3, an anomalous spin-crossover oxide, in the megagauss fields.

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The effects of pressure on antiferromagnetic (AFM) and superconducting phase transitions of 112-type Ca1-xLaxFeAs2 were studied, and the in-plane electrical resistivity rho(ab) was measured with an indenter-type pressure cell. The AFM phase transition temperatures of T-N = 47, 63, and 63 K at ambient pressure for x = 0.18, 0.21, and 0.26 was suppressed by applying pressure P, with superconductivity emerging at critical pressures of P-c similar or equal to 0, 1.5, and 3.4 GPa, respectively. Correspondingly, the slope of T-N against P decreased as dT(N)/P similar or equal to -15 and -2K/GPa for x = 0.21 and 0.26, respectively. Thus, although the AFM phase was stabilized with La doping x, the AFM phase was suppressed by pressure, and superconductivity eventually emerged.

DOI： 10.7566/jpsj.86.113705

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

The comprehensive magnetic field-temperature (H-T) phase diagram of solid oxygen including the theta phase is discussed in the context of the ultrahigh-field measurement and the magnetocaloric effect (MCE) measurement. The problems originating from the short duration of the pulse field, nonequilibrium conditions and MCEs, are pointed out and dealt with. The obtained phase diagram manifests the entropy relation between the phases as S-theta similar to S-alpha < S-beta << S-gamma

DOI： 10.1103/PhysRevB.96.054439

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

The 5d-transition-metal pyrochlore oxide Cd2Re2O7, which was recently suggested to be a prototype of the spin-orbit-coupled metal [Phys. Rev. Lett. 115, 026401 (2015)], exhibits an inversion-symmetry-breaking (ISB) transition at 200 K and a subsequent superconductivity below 1 K at ambient pressure. We study the crystal structure at high pressures up to 5 GPa by means of synchrotron x-ray powder diffraction. A rich structural phase diagram is obtained, which contains at least seven phases, and is almost consistent with the electronic phase diagram determined by previous resistivity measurements. Interestingly, the ISB transition vanishes at similar to 4 GPa where the enhancement of the upper critical field was observed in resistivity. Moreover, it is shown that the point groups at 8 K, probably kept in the superconducting phases, sequentially transform into piezoelectric, ferroelectric, and centrosymmetric structures on the application of pressure.

DOI： 10.1103/PhysRevB.95.020102

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

Potassium-doped picene (K(3.0)picene) with a superconducting transition temperature (TC) as high as 14 K at ambient pressure has been prepared using an annealing technique. The shielding fraction of this sample was 5.4% at 0 GPa. The TC showed a positive pressure-dependence and reached 19 K at 1.13 GPa. The shielding fraction also reached 18.5%. To investigate the chemical composition and the state of the picene skeleton in the superconducting sample, we used energy-dispersive x-ray (EDX) spectroscopy, MALDI-time-of-flight (MALDI-TOF) mass spectroscopy and x-ray diffraction (XRD). Both EDX and MALDI-TOF indicated no contamination with materials other than K-doped picene or K-doped picene fragments, and supported the preservation of the picene skeleton. However, it was also found that a magnetic K-doped picene sample consisted mainly of picene fragments or K-doped picene fragments. Thus, removal of the component contributing the magnetic quality to a superconducting sample should enhance the volume fraction.

DOI： 10.1088/0953-8984/28/44/444001

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

Dissipation inevitably occurs in first-order phase transitions, leading to irreversible heating. Conversely, the irreversible heating effect may indicate the occurrence of the first-order phase transition. We measured the temperature change at the magnetic-field-induced alpha-theta phase transition of solid oxygen. A significant temperature increase from 13 to 37 K, amounting to 700 J/mol, due to irreversible heating was observed at the first-order phase transition. We argue that the hysteresis loss of the magnetization curve and the dissipative structural transformation account for the irreversible heating. The measurement of irreversible heating can be utilized to detect the first-order phase transition in combination with an ultrahigh magnetic fields generated in a time of mu s order.

DOI： 10.7566/JPSJ.85.094601

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

We succeeded in growing single crystals of SrAl4 and related compounds with the BaAl4-type tetragonal structure by the self-flux method, and measured the electrical resistivity, magnetic susceptibility, Hall coefficient, thermoelectric power, and de Haas-van Alphen (dHvA) effect. A plausible characteristic feature of the charge density wave (CDW) was observed below T-CDW = 243 K in SrAl4. We also studied an effect of pressure on the electronic state in SrAl4 by measuring the electrical resistivity and thermoelectric power. T-CDW is found to decrease with increasing pressure, with a rate of dT(CDW)/dP = -12.5 K/GPa. To clarify the Fermi surface nesting, we studied the Fermi surface in SrAl4, which is found to be different from the Fermi surfaces of the similar compounds SrGa4, BaGa4, and BaAl4 without CDW. The Fermi surfaces in these compounds were determined from the dHvA experiments, together with the energy band calculations. (C) 2015 Published by Elsevier B.V.

DOI： 10.1016/j.jallcom.2015.08.193

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.71.1.0_1851

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.71.1.0_2377

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.71.1.0_2294

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.71.1.0_2427

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.71.1.0_2125

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.71.1.0_2124

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DOI： 10.11316/jpsgaiyo.71.2.0_2008

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The temperature dependence of the Hall coefficient of CeIn3 under high pressure has been investigated. The absolute value of the Hall coefficient shows an anomalous increase below T* similar to 80K at ambient pressure. The increase in T* with increasing pressure is similar to the pressure dependence of the characteristic temperature where the resistivity reaches its maximum. The temperature variations below T* at various pressures are well scaled on a single curve that is the formula based on the two-fluid model. No effect of the antiferromagnetic fluctuations observed in CeTIn5 (T = Co, Rh, and Ir) is observed above 2K even near the critical pressure where antiferromagnetic ordering disappears.

DOI： 10.7566/JPSJ.84.123702

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

The mineral tetrahedrite Cu12Sb4S13 exhibits a first-order metal-insulator transition (MIT) at T-MI = 85K and ambient pressure. We measured the 63Cu-NMR at ambient pressure and the resistivity and magnetic susceptibility at high pressures. Cu-63-NMR results indicate a nonmagnetic insulating ground state in this compound. The MIT is monotonically suppressed by pressure and disappears at similar to 1.0 GPa. Two other anomalies are observed in the resistivity measurements, and the pressure-temperature phase diagram of Cu12Sb4S13 is constructed.

DOI： 10.7566/JPSJ.84.093701

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

The phase diagram of solid oxygen in the magnetic-field-temperature (B-T) plane is revealed by magnetization and magnetotransmission measurements. The high-field phase of solid oxygen, which we term the θ phase, is induced at the temperature below 42 K. The transition fields at the α-θ and β-θ transitions are almost temperature independent, with the phase boundary being very steep. This phase boundary indicates that the entropy change is very small at the α-θ and β-θ transitions, in contrast to the entropy-driven β-γ transition at zero field. We argue that the θ phase differs from the high-temperature γ phase in terms of entropy
the molecular rotation is inhibited in the θ phase, whereas permitted in the γ phase. This finding consolidates the novelty of the θ phase.

DOI： 10.1103/PhysRevB.92.064109

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

The pressure dependence of the superconducting transition temperature (T-c) and unit cell metrics of tetragonal (NH3)(y)Cs0.4FeSe were investigated in high pressures up to 41 GPa. The T-c decreases with increasing pressure up to 13 GPa, which can be clearly correlated with the pressure dependence of c (or FeSe layer spacing). The T-c vs. c plot is compared with those of various (NH3)(y)MxFeSe (M: metal atoms) materials exhibiting different T-c and c, showing that the T-c is universally related to c. This behaviour means that a decrease in two-dimensionality lowers the T-c. No superconductivity was observed down to 4.3 K in (NH3)(y)Cs0.4FeSe at 11 and 13 GPa. Surprisingly, superconductivity re-appeared rapidly above 13 GPa, with the T-c reaching 49 K at 21 GPa. The appearance of a new superconducting phase is not accompanied by a structural transition, as evidenced by pressure-dependent XRD. Furthermore, T-c slowly decreased with increasing pressure above 21 GPa, and at 41 GPa superconductivity disappeared entirely at temperatures above 4.9 K. The observation of a double-dome superconducting phase may provide a hint for pursuing the superconducting coupling-mechanism of ammoniated/non-ammoniated metal-doped FeSe.

DOI： 10.1038/srep09477

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

The pressure-temperature-field phase diagram and quantum fluctuation effect were investigated in the itinerant ferromagnet U3P4 by resistivity, ac susceptibility, and Hall effect measurements under high pressure. The zero-temperature ferromagnetic-to-paramagnetic transition is located at P-c similar to 4.0 GPa. The tricritical point exists at P* = 3.8 GPa and T* = 32 K, where the ferromagnetic transition changes from second- to first-order. As a quantum fluctuation effect, the low-temperature resistivity at P-c follows T-5/3 dependence, which was theoretically described in the case of a three-dimensional ferromagnet. This result indicates that the ferromagnetic-to-paramagnetic transition at P-c may be considered as weakly first-order. Another critical behavior, the huge enhancement of rho(0) observed at P-c, cannot be interpreted as the ferromagnetic fluctuation effect. The Hall effect measurements suggest that the magnetic structure in the ordered state changes under high pressure.

DOI： 10.7566/JPSJ.84.024705

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We present detailed investigations on the effects of Ni substitution (x) on Ce(Cu1-xNix)(2)Si-2 with x < 0.3, and a pressure (p) study for x = 0.04(2), 0.05(2), and 0.09(2) by resistivity measurements. The Cu-Ni substitution suppresses both antiferromagnetic fluctuations and superconductivity in CeCu2Si2, and leads to a dramatic crossover from the heavy-fermion (HF) regime to the intermediate-valence(IV) regime with progressive Ni doping. The crossover can be characterized by a marked increase in Kondo temperature evaluated from resistivity, specific heat, and susceptibility measurements. In high-pressure resistivity measurements, the Ni-doped system exhibits similar anomalies to those observed in CeCu2Si2, namely, T-linear dependence, an enhancement of residual resistivity, and a marked decrease in the A coefficient of the T-2-resistivity. Furthermore, we observed an unexpected upturn anomaly in resistivity in the Ni-doped system under high pressure. By constructing the x-p phase diagram of Ce(Cu1-xNix)(2)Si-2, we demonstrate that the crossover from the HF regime to the IV regime can be associated with these characteristic anomalies in resistivity.

DOI： 10.7566/JPSJ.84.024702

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.2.0_1813

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

We examine magnetic ordering in CePd2P2 by neutron-scattering experiment and confirmed a ferromagnetic order at low temperatures. From the neutron-scattering data, the ordered moment is evaluated to be similar to 1.3(3) mu(B) per Ce ion at 3 K and is considered to be parallel to the c-axis. In addition, no evidence of the change in the magnetic structure was observed below T-C within the experimental accuracy. In DC magnetization measurement with an as-grown powder sample and a magnetically aligned sample, a clear magnetic anisotropy in CePd2P2 was observed in both ferromagnetic and paramagnetic phases. To obtain further insight to the large Curie temperature T-C of CePd2P2, we have examined the magnetic properties of GdPd2P2 as a reference material. In DC magnetization measurement, successive magnetic transitions at T-I = 10.6 K and T-II = 7.4 K were observed in GdPd2P2. By comparing the transition temperatures of the Ce and Gd compounds, we argue the origin of the large Curie temperature of CePd2P2.

DOI： 10.1088/1742-6596/592/1/012013

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.11316/jpsgaiyo.70.2.0_1769

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DOI： 10.11316/jpsgaiyo.70.2.0_1989

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DOI： 10.11316/jpsgaiyo.70.2.0_1814

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

We measured the pressure dependence of in-plane resistivity rho(ab) in the recently discovered iron-based superconductor Ca-10(Ir4As8)(Fe2-xIrxAs2)(5), which shows a unique structural phase transition in the absence of magnetic ordering, with a superconducting transition temperature T-c = 16 K and a structural phase transition temperature T-s similar or equal to 100 K at ambient pressure. T-c and T-s are suppressed on applying pressure and disappear at approximately 0.5 GPa, suggesting a relationship between superconductivity and structure. Ca-10(Ir4As8)(Fe2-xIrxAs2)(5) is a rather rare example in which the superconductivity appears only in a low-temperature ordered phase. The fact that the change in the crystal structure is directly linked with superconductivity suggests that the crystal structure as well as magnetism are important factors governing superconductivity in iron pnictides.

DOI： 10.1103/PhysRevB.90.224513

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Pressure dependence of the Ce valence in CeCu2Ge2 has been measured up to 24 GPa at 300 K and to 17 GPa at 18-20Kusing x-ray absorption spectroscopy in the partial fluorescence yield. Asmooth increase of the Ce valence with pressure is observed across the two superconducting (SC) regions without any noticeable irregularity. The chemical pressure dependence of the Ce valence was also measured in Ce(Cu1-xNix)(2)Si-2 at 20 K. Avery weak, monotonic increase of the valence with x was observed, without any significant change in the two SC regions. Within experimental uncertainties, our results showno evidence for the valence transition with an abrupt change in the valence state near the SC II region, challenging the valence-fluctuation mediated superconductivity model in these compounds at high pressure and low temperature.

DOI： 10.1103/PhysRevLett.113.086403

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

Magnetization measurements and magnetotransmission spectroscopy of the solid oxygen alpha phase were performed in ultrahigh magnetic fields of up to 193 T. An abrupt increase in magnetization with large hysteresis was observed when pulsed magnetic fields greater than 120 T were applied. Moreover, the transmission of light significantly increased in the visible range. These experimental findings indicate that a first-order phase transition occurs in solid oxygen in ultrahigh magnetic fields, and that it is not just a magnetic transition. Considering the molecular rearrangement mechanism found in the O-2-O-2 dimer system, we conclude that the observed field-induced transition is caused by the antiferromagnetic phase collapsing and a change in the crystal structure.

DOI： 10.1103/PhysRevLett.112.247201

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DOI： 10.7566/jpscp.3.017004

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Superconducting phases of (NH3)(y)MxFeSe1-z Te-z have been synthesized by the intercalation of metal atoms (M: Li, Na, Ca) into FeSe and FeSe0.5Te0.5 using a low-temperature liquid NH3 technique. The superconducting transition temperature (T-c) is 31.5 K for Na-doped FeSe, and for Li-, Na-, and Ca-doped FeSe0.5Te0.5 it is 26, 22, and 17 K, respectively. The 31.5 K superconducting is the superconducting phase in ammoniated Na-doped FeSe. The T-c is lower than that (onset T-c = 46 K) of the superconducting phase reported previously. The reason why the T-c of this phase is lower is discussed based on the structure. The pressure dependences of T-c in the (NH3)(y)Na0.5FeSe and (NH3)(y)Na0.4FeSe0.5Te0.5 samples have been measured and a negative pressure dependence is observed; i.e., a decrease in lattice constant c leads to a decrease in Tc, consistent with the behavior of (NH3)(y)Cs0.4FeSe reported previously by our group. Furthermore, the magnetic behavior of (NH3)(y)Na0.4FeSe0.5Te0.5 has been fully investigated at different applied magnetic fields (H) to determine the critical magnetic This is a successful metal intercalation into FeSe1-z Te-z (z not equal 0) and an observation of superconductivity.

DOI： 10.1103/PhysRevB.89.144509

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DOI： 10.7566/JPSJ.83.015001

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

Faraday discovered the magnetism of molecular oxygen in 1850, and since then, oxygen has attracted significant interests as a ubiquitous but exotic molecular magnet. In solid oxygen, the magnetic energy through the exchange interaction is comparable to the van der Waals cohesive energy, resulting in a strong spin-lattice correlation. We reported the discovery of a magnetic-field-induced phase transition of solid oxygen using ultrahigh magnetic fields up to 186 T. This is the first experiments demonstrating the phase control through the spin by applying a magnetic field. Magneto-optical absorption measurements of the a phase at low temperatures revealed that visible light absorption suddenly ceases and the background transparency dramatically improves above the critical field. The large hysteresis in these data indicates a first-order transition with a relaxation time on the order of microseconds. The results strongly suggest the reconstruction of the O-2 molecular geometry by the magnetic field, which causes that the antiferromagnetic phase collapses and the field-induced phase should have an isotropic crystal structure. Since all of the known phases of O-2 are induced in high pressure, the discovery of a field-induced phase is noteworthy in the long history of solid O-2 studies.

DOI： 10.1088/1742-6596/568/4/042018

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DOI： 10.7566/JPSCP.3.011081

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DOI： 10.7566/JPSCP.3.015044

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The pressure dependence of the valence of Ce ions in CeCu2Si2 has been investigated by means of X-ray powder diffraction (XRPD) and nuclear quadrupole resonance (NQR) measurements. The high-pressure XRPD measurements were carried out at 12K for CeCu2Si2 and CeCu2Ge2. Precise measurements under smoothly-applied pressure were achieved through the selection of the gasket material of a diamond anvil cell. The jump of the unit cell volume, which was reported previously in CeCu2Ge2, was not observed within the experimental accuracy, indicating the absence of a first-order valance transition. The pressure dependence of Cu-63-NQR frequency nu(Q) measured in CeCu2Si2 was compared with that calculated from the measured lattice parameters. The nu(Q)'s were calculated for the two cases of LaCu2Si2 and CeCu2Si2, corresponding to localized and itinerant cases for 4f electrons, respectively. The measured and calculated slopes d nu(Q)/dP show good agreement. A small but significant deviation from the pressure-linear dependence in nu(Q) was observed in the narrow pressure range of 3.9-4.5 GPa, indicating a valence crossover adjacent to the critical end point.

DOI： 10.7566/JPSJ.82.114701

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Alkali-metal-intercalated FeSe materials, (NH3) yM0.4FeSe (M: K, Rb, and Cs), have been synthesized using the liquid NH3 technique. (NH3)yCs 0.4FeSe shows a superconducting transition temperature (T c) as high as 31.2 K, which is higher by 3.8 K than the Tc of nonammoniated Cs0.4FeSe. The Tcs of (NH 3)yK0.4FeSe and (NH3) yRb0.4FeSe are almost the same as those of nonammoniated K0.4FeSe and Rb0.4FeSe. The Tc of (NH 3)yCs0.4FeSe shows a negative pressure dependence. A clear correlation between Tc and lattice constant c is found for ammoniated metal-intercalated FeSe materials, suggesting a correlation between Fermi-surface nesting and superconductivity. © 2013 American Physical Society.

DOI： 10.1103/PhysRevB.88.094521

Scopus

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Language：English   Publishing type：Research paper (scientific journal)  

The longitudinal magnetoresistance (LMR) of polycrystalline Ce(Cu1-xNix)2Si2 samples is investigated between T = 2 and 15 K up to H = 80 kOe. The application of magnetic field induces anomalous temperature dependence of the resistivity with the power index n &lt
2 for x = 0.12 and 0.14, in which ρ(T) obeys a T 2-law at H = 0 Oe. A sign-change of the LMR from positive (x &lt
0.03) to negative (x &gt
0.03) is observed at 2 K. The negative LMR at 80 kOe is maximized (∼ -4 % at T = 2 K) around x ∼ 0.10 and subsequently disappears at higher Ni concentrations. Disappearance of the positive LMR in lower x region and the negative LMR at higher Ni concentrations implies a collapse of a coherent Kondo lattice state, and a rapid enhancement of Kondo temperature, respectively. Anomalous quantum fluctuations are probably developed around x ∼ 0.10. © 2013 The Korean Physical Society.

DOI： 10.3938/jkps.63.766

Scopus

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

In a model system of an O-2-O-2 dimer confined in the nanopores of Cu-1,4-cyclohexanedicarboxylic acid, the molecular orientation associated with the spin state was observed by precise synchrotron radiation structure analysis. The obtained charge density level structures revealed that the molecular orientation varied with increasing temperature, coupling with the spin states of the O-2-O-2 dimer. The magnetic properties previously reported were consistently explained by the S = 1 dimer model taking into account the molecular arrangements. The obtained gap parameters are different from those of the O-2-O-2 dimer confined in the nanopores of Cu-2,3-pyrazinedicarboxylate-pyrazine, which is explained by the pore deformation due to the adsorption, depending on the pore size and/or flexibility of the coordination polymer.

DOI： 10.7566/JPSJ.82.084703

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Pressure effects on the rattling and superconductivity in the Einstein solids
AxV2Al20 (Ax = Ga0:2, Al0:3, and Y) are investigated by means of electrical resistivity measurements under high pressure. We observed bumps in resistivity at low temperatures only for Ga0:2 and Al0:3, which can be explained by scattering of conduction electrons by local phonons with Einstein temperatures of 8.5 and 22 K, respectively. The bumps gradually fade out with increasing pressure, and the temperature variations of resistivity for Ga0:2 and Al0:3 approach those of Y. This indicates that the low-energy local phonons in the Ga and Al compounds disappear at high pressures. We also observed T2 behavior with large A coefficients in the low-temperature limit for Ga and Al compounds, but not for Y. With increasing pressure, the A coefficient is largely suppressed, while H' c2 ≡ jdHc2=dTj Tc that also reflects the density of states at Fermi energy decreases more slowly. The T2 behavior in Ga and Al compounds probably originates from el-ph scatterings enhanced by rattling of Ga and Al atoms rather than el-el scatterings. An enhancement in the superconducting transition temperatures by the rattling is also demonstrated by comparing the pressure responses of T c between the three compounds. The enhancements of Tc and el-ph interaction λ is relatively small for these Einstein solids in contrast to those of the β-pyrochlore oxides. © 2013 The Physical Society of Japan.

DOI： 10.7566/JPSJ.82.063707

Scopus

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Language：English   Publishing type：Research paper (international conference proceedings)  

Optical absorption spectra of solid oxygen α phase and liquid oxygen were measured in high magnetic fields over 100 T using a single turn coil method. The absorption originates from the bimolecular transition was observed. The spectra strongly reflect the local magnetic interaction between two oxygen molecules. The shape of the absorption spectrum of the α oxygen changed dramatically with increasing magnetic fields, even though the absorption intensity of liquid oxygen simply declined. This difference cannot be explained by only the local magnetic interaction, and we speculate that the field induced lattice distortion plays an important role in the solid oxygen α phase. © 2012 Springer Science+Business Media, LLC.

DOI： 10.1007/s10909-012-0699-z

Scopus

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Language：Japanese   Publisher：The Japan Society of High Pressure Science and Technology  

We review an indenter-type pressure cell, which possesses a maximum pressure of 5 GPa and a sample space of φ1.6×1.6 mm. This pressure cell is available not only for transport measurements but also for ac-susceptibility and NMR measurements. An advantage is the small size being able to change the direction of the pressure cell in the conventional superconducting magnet, which makes it possible to measure the anisotropy against magnetic field.<br>

DOI： 10.4131/jshpreview.22.214

CiNii Article

CiNii Books

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Other Link： https://jlc.jst.go.jp/DN/JALC/10008377707?from=CiNii

The effects of Ni substitution on Ce(Cu1-xNix)2Si2 have been studied by
specific heat and electrical resistivity measurements. The specific heat
measurement has revealed that the enhanced quantum fluctuations around an
antiferromagnetic quantum critical point are markedly suppressed by Ni
substitution, and that the Fermi liquid state recovers in the Nirich region (x
> 0.12). The characteristic T-linear dependence of the resistivity has been
observed at approximately x ~ 0.10 together with a sign of superconductivity.
The variation of n in the form of rho - rho0 = aT^n against Tmax^1, at which
the resistivity peaks, coincides with the case of high-pressure experiments on
pure CeCu2Si2. The anomalous T-linear behavior appears to occur in the
crossover region from the Kondo regime to the valence fluctuation regime rather
than in the conventional antiferromagnetic quantum critical region.

DOI： 10.1143/JPSJ.81.083701

arXiv

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1016/j.ssc.2011.12.034

CiNii Article

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Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1088/1742-6596/391/1/012005

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Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1088/1742-6596/391/1/012012

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

Ca(Fe1-xRhx)(2)As-2 undergoes successive phase transitions with increasing Rh doping in the T = 0 limit. The antiferromagnetic-metal phase with orthorhombic structure at 0.00 &lt;= x &lt;= 0.020 is driven to a superconducting phase with uncollapsed-tetragonal (ucT) structure at 0.020 &lt;= x &lt;= 0.024; a non-superconducting collapsed-tetragonal (cT) phase takes over at x &gt;= 0.024. The breakdown of Fermi-liquid transport is observed in the ucT phase above T-c. In the adjacent cT phase, Fermi-liquid transport is restored along with a disappearance of superconductivity. This interplay of superconductivity and Fermi-liquid transport suggests the essential role of magnetic fluctuations in the emergence of superconductivity in doped CaFe2As2.

DOI： 10.1143/JPSJ.80.103701

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

Strain and resistivity measurements in UIr showed the occurrence of two structural phase transitions under high pressure, indicating the existence of three phases I-III, with slightly different crystal structures. It is suggested that ferromagnetic phases FM1-FM3 emerge in phases I-III, respectively. The pressure-temperature phase diagram was sensitive to the hydrostaticity of pressure. FM3 and superconductivity are observed in the measurements in which Daphne 7373 is used as a pressure-transmitting medium; however they are both absent in the case where petroleum ether is used as a pressure-transmitting medium. These results indicate a close relationship between ferromagnetism and superconductivity.

DOI： 10.1103/PhysRevB.84.054524

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

We report the results of Hall effect measurements on CeCu2Si2 under high pressures up to 4.8 GPa. The Hall coefficient at ambient pressure increases with decreasing temperature and exhibits maximum at 4 K. The Hall coefficient at temperature higher than the coherent temperature of 10 K is consistent with the anomalous Hall effect. The pressure effect on the temperature dependence of the Hall coefficient is not simple. The pressure dependence of the Hall coefficient shows anomaly from 3.1 to 4.8 GPa, where the superconductivity is enhanced. These results indicate the close relationship between the Hall coefficient and the superconductivity.

DOI： 10.1143/JPSJS.80SA.SA061

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

The superconductivity of Cd2Re2O7 is investigated under hydrostatic pressures up to 4.6 GPa by means of electrical resistivity. A rich phase diagram is obtained, which contains at least five new pressure-induced phases in addition to the three already present at ambient pressure, revealing inherent structural and electronic instabilities of the compound. We find large enhancements of more than one order of magnitude in the upper critical field as well as in the coefficient of the T-2 term in resistivity at around a critical pressure of 4.2 GPa, where an inversion-symmetry-breaking structural transition tends to disappear. Heavy fermion superconductivity is probably realized under high pressures in Cd2Re2O7, which is extraordinary for d-electron compounds.

DOI： 10.1143/JPSJ.80.023715

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

Adsorption isotherms of N-2, O-2, CO2, and Xe on a flexible microporous coordination polymer, CPL-2 [Cu-2(pzdc)(2)(bpy)]center dot(pzdc = pyrazine-2,3-dicarboxylate; bpy = 4,4'-bipyridine), possessing bellows-shaped one-dimensional channels were measured. A nonintegral number of each of the N-2, O-2, CO2, and Xe molecules can be accommodated in each unit pore, which indicates that all guest molecules are accommoda dated in the so-called "incommensurate fashion". in situ synchrotron X-ray powder diffraction patterns of CPL-2 with guest molecules were recorded. The unit cells were determined from each pattern. It Was found that the host CPL-2 exhibits different crystal transformation with the accommodation of each guest molecule. This indicates that, even in the case of incommensurate adsorption, the flexible framework of a microporous coordination polymer can transform each pore to suit different guest molecules. (C) 2009 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.micromeso.2009.06.023

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Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

DOI： 10.1007/s10909-009-0084-8

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Other Link： http://link.springer.com/article/10.1007/s10909-009-0084-8/fulltext.html

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

We have measured nuclear quadrupole resonance (NQR) for Cu-63 nuclei under high pressure up to 4.8 GPa. A linear increase in NQR frequency (63)nu(Q) of Cu-63 nuclei was observed below 3 GPa. However, (63)nu(Q) deviates gradually from the linear relation above 3.5 GPa. The downward deviation is associated with a change of valence and consistent with the results of band calculations with the structural parameters under pressure. Antiferromagnetic (AFM) spin fluctuations are drastically suppressed with increasing pressure, whereas T-c increases from 0.7 K at ambient pressure to 1.64K at 4.2 GPa. We have found that bulk superconductivity suddenly disappears at 4.8 GPa accompanied with a rapid decrease in the density of states at the Fermi level.
[GRAPHICS]
These are indenter pressure cells for NQR measurements. (C) 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssb.200983050

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High-field magnetization measurements have been performed at various temperatures on the molecular oxygen adsorbed in a microporous coordination polymer CPL-1. Molecular oxygen with S = 1 forms O2-O2 dimer in the nanochannels of CPL-1. The magnetic properties can be explained by not the S = 1 Heisenberg antiferromagnetic dimer model but the O 2-O2 dimer model taking into account the spin-dependent intermolecular potential. This feature is attributed to the fact that the magnetic interaction between O2 is comparable to the van der Waals force. ? 2010 IOP Publishing Ltd.

DOI： 10.1088/1742-6596/200/2/022018

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We report magnetization, heat capacity and electrical resistivity measurements on CePtZn, which crystallizes in the orthorhombic TiNiSi type structure. Magnetization and electrical resistivity on the iso-structural series of compounds Ce1-xLaxPtZn (x = 0.1, 0.2 0.5 and 1) were also carried out. The electrical resistivity of CePtZn was also measured in external magnetic fields up to 12 T and under pressures up to 2.66 GPa. We find that CePtZn is a dense Kondo lattice, ordering antiferromagnetically at T-N = 1.7 K, with a comparable Kondo temperature. The magnetic transition temperature, T-N, is continuously suppressed both by the magnetic field and pressure and T-N. 0 around 5-6 T and at 1.2 GPa, respectively. Non-Fermi liquid behavior of resistivity at 4 T and 1.2 GPa and logarithmic divergence of the heat capacity, C-4f/T, at 6 T in a limited temperature region strongly suggest the emergence of a quantum critical point as T-N -&gt; 0.

DOI： 10.1088/0953-8984/21/15/156001

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：POLISH ACAD SCIENCES INST PHYSICS  

We studied pressure effects on YbCu(5) and YbInCu(4), good examples of the Yb-based compounds to investigate the nonmagnetic-magnetic transition in Yb-based strongly correlated electron systems. With increasing pressure, the low-temperature Fermi liquid state of YbCu(5) is gradually suppressed, suggesting the second-order like nonmagnetic-magnetic transition around the pressure of 5-6 GPa. On the other hand, in YbInCu(4) which has a pressure-induced magnetic ordered ground state above P(C) = 2.45 GPa, both high-temperature paramagnetic and low-temperature intermediate valence phases are insensitive to pressure. Our results confirm the first-order nature of the transition between the intermediate valence and magnetic ordered phases with pressure.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER SCIENTIFIC PUBLISHERS  

The crystal structure of a microporous coordination polymer with adsorbed methane gas was determined by in situ synchrotron powder diffraction of the gas adsorption and the MEM (maximum entropy method)/Rietveld method. Methane molecules were found to be adsorbed forming a one-dimensional array in the nanochannels of the polymer. The MEM charge density distribution of the adsorbed methane molecules indicated some protrusions which were not observed in that of a spherical atom of adsorbed argon. This was interpreted as a mixed distribution of two uniaxially rotating molecules with different pivotal axes. The methane molecules displayed hindered rotation depending on the shape of the nanopore surface. This result indicates the capability to control the molecular arrangement and orientation by the adsorption of gas molecules on the precisely designed nanopores of coordination polymers.

DOI： 10.1166/jnn.2009.J085

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.64.1.3.0_546_4

CiNii Article

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

We report the results of Cu-63 nuclear quadrupole resonance (NQR) measurements on CeCu2Si2 under high pressures up to 4.8GPa. Enhanced spin fluctuations due to quantum criticality at ambient pressure are drastically suppressed with increasing pressure, whereas T-c increases from 0.7 K at ambient pressure to 1.64K at 4.2GPa. We have found that bulk superconductivity suddenly disappears at 4.8GPa accompanied with a rapid decrease in the density of states at the Fermi level. The nuclear spin-lattice relaxation rate 1/T-1 at 4.2 GPa reveals that anisotropic superconductivity in the strong-coupling regime is realized even under high pressure far from the antiferromagnetic critical point. Superconductivity under high pressure is unconventional in origin, but the spin fluctuation scenario is not likely to be applicable.

DOI： 10.1143/JPSJ.77.123711

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

We report pressure-induced superconductivity in antiferromagnetic cerium compounds and a ferromagnetic uranium compound, focusing on the relation between the superconducting state and the Fermi surface instability in CeRhIn5 and the huge upper critical field H-c2 in CeIrSi3 without inversion symmetry in the crystal structure. The pairing interaction is well correlated with ferromagnetism, as well as antiferromagnetism or antiferromagnetic fluctuations. In the recently discovered superconductor NpPd5Al2, superconductivity is found to be located in the vicinity of an antiferromagnetically ordered state. The upper critical field H-c2 is strongly supressed by the large paramagneic effect, and the corresponding magnetization curve indicates a step-like increase at H-c2, producing a first-order phase transition.

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

Elastic neutron-scattering and ac-susceptibility measurements have been performed on a 20 single crystal of URu2Si2 under hydrostatic pressure up to similar to 1.1 GPa using Fluorinert 70 & 77 and Daphne oil 7373 as pressure-transmitting media. Daphne oil produces better hydrostaticity of the applied pressure than Fluorinert, resulting in a slight shift of the phase boundary between hidden order and antiferromagnetic order to a lower pressure. The superconducting phase is also influenced, but never overlaps with the antiferromagnetic phase. (c) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2007.10.065

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

We report that the nuclear spin-spin relaxation rate 1/T-2 shows characteristic peaks in the skutterudite compounds of ROs4Sb12 (R = La, Pr, Nd, and Sm) and PrRu4Sb12. The broadening of Sb-NQR spectrum accompanied with the peak in 1/T-2 suggests that some charge fluctuation exists in these systems and slows down around the peak in 1/T-2. The peaks in 1/T-2 appear around 120 K in all the systems we measured, while the other peaks around 20 K are observed in ROs4Sb12 (R = Pr, Nd, and Sm). The 12 Sb sites are not equivalent at low temperatures in these compounds. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2007.10.226

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

We have investigated evolution of transport and low-energy spin fluctuation properties of heavy Fermi liquid compounds YbAuCu4 and YbPdCu4 with the application of magnetic field. YbAuCu4 is found to be driven from the originally antiferromagnetically (AFM) ordered ground state (T-N similar to 0.8K) to a nonmagnetic Fermi liquid (FL) one through the field-tuned quantum critical point (QCP) at H-cr similar or equal to 13 kOe (T-N -&gt; 0). In the vicinity of H-cr, the electrical resistivity measurement provides evidence for the increase in the inelastic scattering of heavy electrons, and the Cu-63 Spin-lattice relaxation rate measurement exhibits the occurrence of AFM spin order instability. Whilst, YbPdCu4 transforms from the originally ferromagnetically (FM) ordered ground state (T-C similar to 0.6K) into the nonmagnetic FL state, without any intermediate NFL phenomena. This result indicates that the competition of the field-stabilized FM correlation and field-destabilized AFM correlation plays an important role on the field-driven quantum critical phenomena. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2007.10.325

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

We have succeeded in observing the de Haas-van Alphen effect in PrOs4P12 which shows no anomaly down to 50 mK in contrast to PrFe4P12 and PrRu4P12. The Fermi surface (FS) topology is reasonably explained by the energy band structure calculation based on a full potential linearized augmented-plane-wave method within the local-density-approximation. Whereas the localized nature of 4f-electrons, we have confirmed a highly enhanced cyclotron effective mass up to 18m(0) in PrOs4P12, which is enhanced 3.8 times compared to that of LaOs4P12. No nesting property with q = (1, 0, 0) in the FS of PrOs4P12 has been confirmed, which suggests both the 4f-electron's contribution and the FS nesting property play the role for the phase transitions in PrFe4P12 and PrRu4P12.

DOI： 10.1143/JPSJS.77SA.108

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

We report resistivity, nuclear quadrupole resonance (NQR), and magnetization measurements under high pressures in a novel heavy fermion compounds SmOs4Sb12. The resistivity and nuclear spin-lattice relaxation rate 1/T-1 show the coherent behavior below a characteristic temperature T* = 20 - 25 K at ambient pressure. Nuclear spin-spin relaxation rate 1/T-2 was found to show a peak of electrical origin around T*. Some charge fluctuation is considered to play an important role in the Kondo effect of SmOs4Sb12. On the other hand, the magnetization at low temperature does not increase under pressures, although the transition temperature increases. The NQR signals are strongly suppressed around the transition temperature and vanishes at low temperatures. These suggest that the ordered state in SmOs4Sb12 is not simple ferromagnetism.

DOI： 10.1143/JPSJS.77SA.90

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

We report Sb-123 nuclear quadrupole resonance (NQR) measurements of the filled skutterudite heavy-fermion superconductor PrOs4Sb12 under high pressure. The temperature dependence of NQR frequency and spin-lattice relaxation rate 1/T-1 indicate that the crystal electric field splitting Delta(CEF) between the ground state Gamma(1) singlet and the first excited state Gamma((2))(4) 4 triplet decreases with increasing pressure. However, it is found Delta(CEF) and T-c stay constant above P similar to 2 GPa revealed by Sb-NQR up to P = 3.82 GPa for the first time. Remarkably, the temperature dependence of 1/T1 below T-c = 1.55 K at P = 1.91 GPa shows no coherence peak just below Tc and power-law behavior well below Tc in contrast to the exponential decrease observed at P = 0. Present results indicate the superconductivity in PrOs4Sb12 under pressure has nodes in the superconducting gap function.

DOI： 10.1143/JPSJS.77SA.330

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DOI： 10.1103/PhysRevB.77.064508

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Language：English   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.1143/JPSJ.77.025001

CiNii Article

CiNii Books

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-BLACKWELL  

DOI： 10.1002/anie.200705822

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Language：English   Publisher：ELSEVIER SCIENCE SA  

Microporous coordination polymers have attracted attention for their numerous nanotechnology and engineering applications. Nano-coordination space provides some unique properties and functions that could never be realized in conventional porous materials. For the strategy of rational designs and the syntheses of novel porous coordination polymers, the structural information of adsorbed guest molecules inside the nanopores and the host framework is very important. In the present study, we describe the technique of the direct observation of gas molecules adsorbed in the nanochannels of porous coordination polymers by the in situ synchrotron powder diffraction measurement of gas adsorption and the maximum entropy method (MEM)/Rietveld charge density analysis. Specific alignment and properties of molecular oxygen obtained by gas adsorption in the nano-coordination space are revealed. (C) 2007 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.ccr.2007.07.025

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

We report Sb-121,Sb- 123 nuclear quadrupole resonance measurements under pressure in a novel heavy fermion (HF) system SmOs4Sb12. The nuclear spin-spin relaxation rate 1/T-2 exhibits a distinct peak near the coherent temperature of the Kondo effect. The isotope effect of Sb-121 and Sb-123 indicates that the peak in 1/T-2 is electrical in origin. The connection between the peak in 1/T-2 and the development of coherency of the Kondo effect is robust even under pressure. It is conjectured that charge fluctuation plays an important role in forming the HF state in SmOs4Sb12.

DOI： 10.1103/PhysRevLett.99.156408

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

Pressure-induced superconductivity is found in UIr without inversion symmetry. The pressure-temperature phase diagram has been investigated by means of the electrical resistivity, ac-susceptibility and magnetization measurements under high pressure. The phase diagram consists of three magnetic phases FM1-3 and a superconducting phase. The huge enhancement of residual resistivity and the negative magnetoresistance are found in the intermediate pressure region. These behavior may be induced by the pressure-induced structural phase transition and the accompanied phase separation in this pressure range. The superconducting phase with narrow pressure range is embedded in the FM3 phase, adjacent to zero-temperature FM3-to-nonmagnetic transition. The temperature dependence of resistivity above T-SC follows non-Fermi liquid form of T-1.6. From these experimental facts, superconductivity is considered to be associated with the ferromagnetic fluctuation.

DOI： 10.1143/JPSJ.76.051007

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

We have studied the pressure-temperature phase diagrams in UIr, U3P4, UP2, CeAgSb2 and CeMg2Cu9 by means of the electrical resistivity. Application of pressure suppresses the magnetic ordering shown at ambient pressure in all compounds. In UIr, the pressure-induced superconductivity is observed in the vicinity of the magnetic-nonmagnetic transition. In this article, we review the pressure-temperature phase diagram and the properties of the magnetic nonmagnetic transition in these compounds.

DOI： 10.1088/0953-8984/19/12/125205

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

We studied the change of the Fermi surface properties in antiferromagnets CeIn3 and CeRhIn5 via the dHvA experiments under pressure. We found the abrupt change of the Fermi surface at the critical pressure P-c, where the magnetic ordering state changes to the paramagnetic one. The change of the Fermi surface indicates that the 4f-electron character is changed from localized to itinerant in CeIn3 and CeRhIn5 at P-c. Namely, the 4f-electron contributes to the volume of the Fermi surface above P-c. Interestingly, the pressure-induced heavy fermion state with large effective mass was observed around P-c, where the pressure-induced superconductivity appears. We also discuss the Fermi surface properties in the system without inversion symmetry in the crystal structure as in CePt3Si and CeTX3 (T:Co, Ir, Rh, X: Si, Ge). The spin-orbit interaction due to the lack of inversion symmetry brings about a splitting of the Fermi surface, which is important for considering the formation of Cooper pair. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.11.197

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

We report 73 Ge-nuclear-quadrupole resonance (NQR) study of heavy-fermion compound CeNi2Ge2. The temperature dependence of the 73 Ge nuclear-spin-lattice-relaxation rate 1/T-1 indicates the development of magnetic correlations and the formation of a Fermi-liquid state at temperatures lower than T-FL 0.4K, where 1/T1T is constant. The 1/T1T decrease below T(NQR)c 0.1K, whereas resistance decreases below T (onset)c = 0.2K and does not become zero. These results indicate CeNi2Ge2 closely locates to a superconducting quantum critical point. (c) 2006 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.232

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

UIr crystallizes in the monoclinic crystal structure without inversion symmetry. The magnetization measurement indicated that UIr is an Ising-type ferromagnet with the Curie temperature T-C1 = 46K at ambient pressure. We grew a high-quality single crystal by the Czochralski method in a tetra-arc furnace. The ingot was annealed under high vacuum by the solid state electrotransport method. Superconductivity with a transition temperature T-sc = 0.14 K was found under pressure. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.292

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

We have carried out electrical resistivity measurements on PrFe4P12 under high pressure using some kinds of pressure-transmitting mediums in order to investigate the effect of uniaxial stress on a pressure-induced metal-insulator (M-I) transition. In the measurement under uniaxial stress, the M-I transition appears at a lower pressure than in the case of quasi-hydrostatic pressure, indicating that the uniaxial stress is favorable to the insulating phase. On the other hand, the M-I transition appears suddenly with finite M-I transition temperature between 2.55 and 2.66 GPa in the measurement under hydrostatic pressure. This fact suggests that the transition from the antiferroquadrupolar metallic phase to the insulating phase is of first order. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2006.10.1074

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

An indenter-type high-pressure cell has been developed for electric and magnetic measurements in low-temperature and high-magnetic-field environments. The maximum pressure achieved at low temperatures is more than 4.5 GPa, which is higher than that of a conventional piston-cylinder cell. The typical sample space at maximum pressure is 1.6 mm in diameter and approximately 0.7 mm in depth, and magnetic measurements such as ac-susceptibility and nuclear magnetic resonance can be performed using a miniature coil. All the components of the indenter cell are made of nonmagnetic materials that have enough thermal conductivity for low-temperature experiments using a He-3/He-4 dilution refrigerator. Another indenter-type cell designed for a commercial superconducting quantum interference device magnetometer is also reported. (c) 2007 American Institute of Physics.

DOI： 10.1063/1.2459512

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

We have studied the physical properties of a pressure-induced insulating phase in PrFe4P12 via Hall effect, P-31-NMR and magnetization measurements under quasi-hydrostatic pressure. In the Hall effect measurement, a decrease in the number of hole carriers due to the metal-insulator (M-I) transition is confirmed, indicating a band insulating state. The P-31-NMR spectrum exhibits abrupt broadening and the susceptibility is suppressed markedly owing to the M-I transition, suggesting that an antiferromagnetic ordering occurs in the insulating phase and the M-I transition is of first order. Both spectra corresponding to the metallic and insulating phases are observed simultaneously in a wide temperature range near the M-I transition. This fact reflects the sensitivity of the M-I transition to uniaxial stress, which is confirmed in the resistivity measurement under uniaxial stress.

DOI： 10.1143/JPSJ.75.094709

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

An antiferromagnet CeNiGe3, which exhibits a quantum critical point at P-C-6-7 GPa, shows the superconductivity in wide pressure range of 1.7-9.3 GPa. In addition to the superconductivity around P-C, the sharp Superconducting transition can be observed by both the resistivity and the susceptibility measurements at lower pressure region far apart from P-C, where 4f-localized Picture seems to be still dominant. Such a superconductivity is a first example in the f-electron systems. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.phys.2006.01.147

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High-pressure AC-susceptibility measurement has been carried out in UIr. Three series of peaks corresponding to the successive ferromagnetic transitions indicate the existence of three ferromagnetic phases FM 1-3. The phase boundary between FM2 and FM3 was not realized in the resistivity measurement. The Meissner effect is observed successfully in the pressure range of 2.63-2.74 GPa where the peak of AC-susceptibility survives. This result indicates that the superconducting phase is embedded in the FM3 phase with the ordered moment less than 0.051 mu(B)/U and adjoins the quantum critical point. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2006.01.26

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CeAgSb2 crystallizes in the tetragonal ZrCuSi2 type structure (P4/nmm), which consists of Sb-Ce, Sb-Ag-Ce, Sb-Sb layers. It shows the peculiar anisotropic ferromagnetic ordering below 9.7 K with a small ordered moment of 0.33 mu B. Its residual resistivity steeply increases above p(c) congruent to 3.3 GPa where the magnetic order disappears. It is expected that the p-f mixing on the peculiar hollow square pillar-like Fermi surface plays an important role in CeAgSb2, while similar Fermi surfaces were not observed in LaAgSb,. We have measured the anisotropy in the electrical resistivity of CexLa1-xAgSb2 to study the p-f mixing effect. Small humps were observed in the temperature dependence of the resistivity in (CeLa1-xAgSb2)-La-x. We expected them the CDW transition. The CDW state coexisted with the ferromagnetic state around x = 0.2. (c) 2006 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2006.01.305

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We present evidence for unconventional superconducting fluctuations in a heavy-fermion compound CeNi2Ge2. The temperature dependence of the Ge-73 nuclear-spin-lattice-relaxation rate 1/T-1 indicates the development of magnetic correlations and the formation of a Fermi-liquid state at temperatures lower than T-FL = 0.4 K, where 1/T1T is constant. The resistance and 1/T1T measured on an as-grown sample decrease below 7(c)(onset) = 0.2 K and T-c(NQR) = 0.1 K, respectively: these are indicative of the onset of superconductivity. However, after annealing the sample to improve its quality. these superconducting signatures disappear. These results are consistent with the emergence of unconventional superconducting fluctuations in close proximity to a quantum critical point from the superconducting to the normal phase in CeNi2Ge2.

DOI： 10.1143/JPSJ.75.043702

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We carried out the de Haas-van Alphen (dHvA) measurement and the pressure experiment of the electrical resistivity for an antiferromagnet Ce3Sn7 with the orthorhombic crystal structure. The detected dHvA branches are many in number and their dHvA frequencies are extremely small in magnitude, indicating that Ce3Sn7 is a semimetal. This is consistent with the result of the energy band calculations under the assumption that the 4f electrons of two Ce atoms in the 2(a) site are localized and the 4f electron of one Ce atom in the 4(i) site is itinerant. In the pressure experiment, the Neel temperature of T-N = 5.3 K is found to slightly increase with increasing pressure, becomes maximum around 1 GPa, then decreases steeply with further increasing pressure and most likely becomes zero between 3 and 4GPa. The anti ferromagnetic state is changed into the non-magnetic state under pressure.

DOI： 10.1143/JPSJ.75.044715

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

Specific-heat experiments on single crystals of the S=1 quasi-one-dimensional bond-alternating antiferromagnet Ni(C9H24N4)(NO2)ClO4 (NTENP) have been performed in magnetic fields applied both parallel and perpendicular to the spin chains. We have found for the parallel field configuration that the magnetic specific heat (C-mag) is proportional to temperature (T) above a critical field H-c, at which the energy gap vanishes, in a temperature region above that of the long-range ordered state. The ratio C-mag/T increases as the magnetic field approaches H-c from above. The data are in good quantitative agreement with the prediction of the c=1 conformal field theory in conjunction with the velocity of the excitations calculated by a numerical diagonalization, providing conclusive evidence for a Tomonaga-Luttinger liquid.

DOI： 10.1103/PhysRevLett.96.147203

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The antiferromagnet CeNiGe3 exhibits superconductivity under pressure. The Neel temperature initially increases with increasing pressure up to 3GPa and then becomes zero at a critical pressure (P-C) that is located at approximately 7GPa. We found that superconductivity emerges from 1.7 GPa in the antiferromagnetic (AF) phase removed from P-C. The superconductivity is realized in a wide pressure region including P-C. The coefficient A in the resistivity and the upper critical field (H,2) significantly change against pressure. A feature of CeNiGe3 is that the moderate heavy fermion state in the AF phase induces superconductivity.

DOI： 10.1143/JPSJ.75.044713

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Anisotropic resistivity in UIr has been investigated under high pressure. A huge enhancement of residual resistivity was found under high pressure for the measuring current parallel to the [0 1 0] direction while any anomalies were not observed in the resistivity for [1 0 (1) over bar]. The residual resistivity for [0 1 0] reduced to the original value in the pressure range where superconductivity appears. This anomalous behavior indicates that the ground state in the high-rho(0) state is not simple ferromagnet and the application of pressure induces the first-order transition to slightly different electronic state.

DOI： 10.1143/JPSJS.75S.82

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Language：Japanese   Publisher：The Physical Society of Japan  

DOI： 10.11316/jpsgaiyo.61.1.3.0_554_1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

DOI： 10.1002/anie.200600976

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

Molecules and atoms confined in a nanospace may have properties distinctly different from those of the bulk fluid, owing to the formation of a specific molecular array characteristic of nanospace. In situ synchrotron powder X-ray diffraction measurements have been used to observe confined guest molecules such as N(2), O(2), Ar, and CH(4) in the well-regulated ultramicropore of a copper coordination polymer, 1 ([Cu(2),(pzdc)(2)pyz]: pzdc = 2,3-pyrazinedicarboxylate and pyz = pyrazine). The obtained crystal structures indicate that guest molecules are confined in a linear fashion to form crystal ine-like regular ordered arrays, in contrast to the situation in the gas and liquid state, even at temperatures above the boiling point, and the ordered arrays are characteristic of the kind of gas molecule and the geometrical and potential properties of the ultramicropore of 1.

DOI： 10.1021/jp054411j

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

We have studied a change of the Fermi surface in an antiferromagnet CeIn3 via the de Haas-van Alphen experiment under pressure up to 3 GPa. With increasing pressure P, the Neel temperature T-N = 10 K decreases and becomes zero at a critical pressure P-c similar or equal to 2.6 GPa. In the pressure region P &gt; P,, we have observed a large main Fermi surface named a, which indicates that the electronic state of 4f electron in CeIn3 changes from localized to itinerant at P-c, as observed in the similar antiferromagnets CeRh2Si2 and CeRhIn5. The cyclotron effective mass m(c)(*) of this main Fermi surface is extremely enhanced around P-c: m(c)(*) similar or equal to 60m(0) at 2.7 GPa for the magnetic field along the (100) direction.

DOI： 10.1143/JPSJ.74.3016

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

We have succeeded in growing a high-quality single crystal of an antiferromagnet UPdGa5 by the Ga-flux method with the off-stoichiometric composition of U : Pd : Ga = 1 : 2 : 7.3. The Neel temperature T-N = 30.5 K is found to increase with increasing the residual resistivity ratio (RRR) and becomes constant for a high-quality single crystal sample whose RRR is larger than 50. The electronic state has been investigated by the de Haas-van Alphen experiment, indicating the similar cylindrical Fermi surfaces as in an antiferromagnet UPtGa5. We have also studied the pressure effect by measuring the electrical resistivity. The Neel temperature decreases with increasing pressure and becomes zero at 3.1 GPa. The antiferromagnetic state is changed into the paramagnetic state above 3.1 GPa.

DOI： 10.1143/JPSJ.74.2277

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

We report nuclear quadrupole resonance (NQR) measurement at ambient pressure and resistivity measurement under high pressure in the new heavy fermion (HF) compound SmOs4Sb12. The NQR spectrum and the nuclear spin-lattice relaxation rate (1/T-1) clearly demonstrate the bulk nature of ferromagnetic ordering below T-C similar to 2 K. The temperature dependence of 1/T-1 exhibits the characteristic behaviors of a Kondo lattice. The application of pressure decreases Kondo temperature and stabilizes the magnetic ordering, which is the same tendency as that found in some Yb-based compounds. The obtained phase diagram indicates SmOs4Sb12 to be in the vicinity of its ferromagnetic critical point.

DOI： 10.1143/JPSJ.74.2173

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：NATURE PUBLISHING GROUP  

Metal - organic microporous materials(1-4) (MOMs) have attracted wide scientific attention owing to their unusual structure and properties, as well as commercial interest due to their potential applications in storage(5-9), separation(10,11) and heterogeneous catalysis(12,13). One of the advantages of MOMs compared to other microporous materials, such as activated carbons, is their ability to exhibit a variety of pore surface properties such as hydrophilicity and chirality, as a result of the controlled incorporation of organic functional groups into the pore walls(11,13-15). This capability means that the pore surfaces of MOMs could be designed to adsorb specific molecules; but few design strategies for the adsorption of small molecules have been established so far. Here we report high levels of selective sorption of acetylene molecules as compared to a very similar molecule, carbon dioxide, onto the functionalized surface of a MOM. The acetylene molecules are held at a periodic distance from one another by hydrogen bonding between two non-coordinated oxygen atoms in the nanoscale pore wall of the MOM and the two hydrogen atoms of the acetylene molecule. This permits the stable storage of acetylene at a density 200 times the safe compression limit of free acetylene at room temperature.

DOI： 10.1038/nature03852

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Language：English   Publishing type：Research paper (international conference proceedings)  

We have investigated a change of the electronic state in CeIn3 via de Haas-van Alphen (dHvA) experiments under pressure up to 2.72 GPa for the magnetic field along 〈110〉. A main Fermi surface with the dHvA frequency F=9.4×107 Oe and a large cyclotron mass mc*=53m0 was observed at 2.72 GPa in the vicinity of the critical pressure where the Néel temperature is suppressed to zero. © 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.01.119

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

Magnetization measurements of URu2Si2 have been performed under hydrostatic pressures. The superconducting transition temperature decreases linearly with pressure up to 1.1 GPa and disappears above 1.5 GPa. The hysteretic magnetization shows characteristic behaviors at high pressures, suggesting that the pinning properties are changed due to the switch of the normal state to the antiferromagnetic state. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.01.325

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We have studied the electrical resistivity in a skutterudite compound PrFe4P12 under high pressure. An antiferroquadrupolar ordering temperature T-Q decreases monotonously with increasing pressure up to 2.4 GPa. Above 2.4 GPa, the metal-insulator (M-I) transition appears. By applying magnetic field, this M-I transition is suppressed easily and heavy-fermion state is realized. The observed Kondo effect and the field-induced heavy-fermion state at high pressure suggest that the quadrupolar interactions of the f electrons of Pr3+ survive even in the insulator phase. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.01.334

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We have measured the electrical resistivity of antiferromagnetic Kondo compounds CeNiGe3 and CeNi2Al5 under pressure. In CeNiGe3, Neel temperature T-N initially increases with increasing pressure P up to 3 GPa, then decreases rather steeply with further increasing pressure, and becomes zero at a critical pressure P-c similar or equal to 5.5 GPa. The A and rho(0) values of the resistivity rho = rho(0) + AT(2) in the Fermi liquid relation become maximum around P-c. Superconductivity is found below 0.48 K in a wide pressure region from 4 to 10 GPa. In CeNi2Al5, the similar pressure dependence of TN is found, has a maximum at 3.9 GPa, and becomes zero around 6 GPa. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/i.physb.2005.01.066

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The powder X-ray diffraction experiments of LiV2O4 have been performed at low temperature and high pressure using synchrotron radiation. In the isothermal experiment at 10 K, the cubic-rhombohedral phase transition corresponding to the metal-insulator transition is found at around 13 GPa. This transition seems to be due to charge ordering of V ions on the analogy of the metal-insulator transition in AlV2O4. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.01.390

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Pressure-induced superconductivity is found in UIr without inversion symmetry. The pressure-temperature phase diagram has been investigated by means of electrical resistivity and magnetization. The phase diagram consists of two ferromagnetic phases. The ferromagnetic phase FM1 with T-Cl similar to 46 K at ambient pressure disappears around 1.7 GPa. With further increase of pressure, the phase (FM2) with small ferromagnetic moment appears in the pressure range of P-Cl &lt; P &lt; 2.6 GPa. The superconducting phase exists near the disappearance point of the FM2 phase, indicating that the superconductivity is associated with the ferromagnetic critical fluctuation around P-C2. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physb.2005.01.335

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

We have studied the electrical resistivity of the filled skutterudite compound PrFe4P12 under high pressure. The antiferroquadrupolar ordering temperature T-Q decreases monotonically with increasing pressure up to 2.4 GPa. Above 2.4 GPa, we have found that a metal-insulator (M-I) transition appears. The insulating state is easily suppressed by a magnetic field. The observed Kondo effect and a field-induced heavy-fermion state at high pressure suggest that the quadrupolar interactions survive in the insulating region. The quadrupolar interactions might play an essential role in the M-I transition. PrFe4P12 is an unusual compound in that it shows a pressure-induced transition from a metal to an insulator.

DOI： 10.1103/PhysRevB.71.073102

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Publishing type：Research paper (scientific journal)  

We have studied the electrical resistivity of the filled skutterudite compound PrFe 4P 12 under high pressure. The antiferroquadrupolar ordering temperature T Q decreases monotonically with increasing pressure up to 2.4 GPa. Above 2.4 GPa, we have found that a metal-insulator (M-I) transition appears. The insulating state is easily suppressed by a magnetic field. The observed Kondo effect and a field-induced heavy-fermion state at high pressure suggest that the quadrupolar interactions survive in the insulating region. The quadrupolar interactions might play an essential role in the M-I transition. PrFe 4P 12 is an unusual compound in that it shows a pressure-induced transition from a metal to an insulator. ©2005 The American Physical Society.

DOI： 10.1103/PhysRevB.71.073102

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DOI： 10.1002/anie.200461895

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE  

The magnetic properties of O-2 adsorbed in nanochannels of porous metal-organic solids CPL-1 and CPL-p1 have been investigated by means of high-field magnetization process measurement. The contribution from adsorbed 02 shows the metamagnetic-like behavior in both compounds. We propose "the field-induced rearrangement mechanism" as the explanation for the metamagnetic-like behavior. It is known for the O-2-O-2 dimer that the magnetic interaction depends strongly on the intermolecular distance and the orientation of molecular axes. It is considered naturally that the stable arrangement with saturated magnetic moment in the sufficient high field is different from the H-structure which is stable at zero field.

DOI： 10.1143/PTPS.159.271

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We have measured the electrical resistivity, thermoelectric power, Hall coefficient, and magnetoresistance (MR) on single crystals of PrOs4Sb12, LaOs4Sb12, and NdOs4Sb12. All the transport properties in PrOs4Sb12 are similar to those in LaOs4Sb12 and NdOs4Sb12 at high temperatures, indicating the localized character of 4f electrons. The transverse MR both in LaOs4Sb12 and PrOs4Sb12 tends to saturate for wide field directions, indicating these compounds to be uncompensated metals with no open orbit. We have determined the phase diagram of the field induced ordered phase by the MR measurement for all the principle field directions, which indicates an unambiguous evidence for the Γ1 singlet crystalline electric field ground state. © 2005 The American Physical Society.

DOI： 10.1103/PhysRevB.72.014519

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

In situ synchrotron X-ray powder diffraction patterns of porous coordination polymers {[Cu-2-(pzdc)(2)(bpy)](.)G} have been measured (pzdc = pyrazine-2,3-dicarboxylate, bpy = 4,4'-bipyridine) (where G = H2O for CPL-2 superset of H2O, G = benzene for CPL-2 superset of benzene, and G = void for the apohost). The structures of apohost and CPL-2 superset of benzene were determined from Rietveld analysis. Adsorption of benzene in the channels induced a remarkable contraction in the crystal (b axis; 6.8%, volume; 4.9%), although the channels were occupied by the benzene molecules. This crystal transformation provides a new pore structure that is well suited for benzene molecules, and we denote it as a "shape-responsive fitting" transformation. This type of pore gives rise to a new guideline: frameworks can be composed of flexible motifs that are linked via strong bond and/or stiff motifs that are connected via weaker bonds.

DOI： 10.1021/ja046925m

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

Pressure-induced superconductivity is found in UIr without inversion symmetry. The pressure-temperature phase diagram has been investigated by means of the electrical resistivity and magnetization measurements under high pressure. The phase diagram consists of two magnetic phases, the Ising-like ferromagnetic phase (FM1) at low pressures and another magnetic phase (FM2) with the small ferromagnetic component along the [101] direction at high pressures. Superconductivity is observed in the narrow pressure range near the disappearance point of the FM2 phase, where the temperature dependence of resistivity follows the non-Fermi liquid form of T-1.6. From these experimental facts, the superconductivity is considered to be associated with the critical fluctuation with the disappearance of FM2 phase.

DOI： 10.1143/JPSJ.73.3129

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Language：English   Publishing type：Research paper (international conference proceedings)  

DOI： 10.1142/9789812702517_0051

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

A new three-dimensional (3-D) jungle-gym-like open metal-organic framework has been synthesized from a two-dimensional (2-D) layer compound using a heterogeneous pillar insertion reaction. Both the starting 2-D layer and the resulting 3-D open compounds have been characterized using X-ray crystallography.

DOI： 10.1021/ic049005d

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

The heat-capacity and magnetization measurements under high pressure have been carried out in a ferromagnetic superconductor UGe2. Both measurements were done using a same pressure cell in order to obtain both data for one pressure. Contrary to the heat capacity at ambient pressure, an anomaly is found in the heat capacity at the characteristic temperature T-* where the magnetization shows an anomalous enhancement under high pressure where the superconductivity appears. This suggests that a thermodynamic phase transition takes place at T-* at least under high pressure slightly below P-c(*) where T-* becomes zero. The heat-capacity anomaly associated with the superconducting transition is also investigated, where a clear peak of C/T is observed in a narrow pressure region (DeltaPsimilar to0.1 GPa) around P-c(*) contrary to the previous results of the resistivity measurement. Present results suggest the importance of the thermodynamic critical point P-c(*) for the appearance of the superconductivity.

DOI： 10.1103/PhysRevB.69.180513

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The heat-capacity and magnetization measurements under high pressure have been carried out in a ferromagnetic superconductor UGe2. Both measurements were done using a same pressure cell in order to obtain both data for one pressure. Contrary to the heat capacity at ambient pressure, an anomaly is found in the heat capacity at the characteristic temperature T* where the magnetization shows an anomalous enhancement under high pressure where the superconductivity appears. This suggests that a thermodynamic phase transition takes place at T* at least under high pressure slightly below P*c where T* becomes zero. The heat-capacity anomaly associated with the superconducting transition is also investigated, where a clear peak of C/T is observed in a narrow pressure region (ΔP∼0.1 GPa) around P* contrary to the previous results of the resistivity measurement. Present results suggest the importance of the thermodynamic critical point P*c for the appearance of the superconductivity.

DOI： 10.1103/PhysRevB.69.180513

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We have investigated a change of the electronic state in CeIn3 via de Haas-van Alphen (dHvA) experiments under pressure up to 2.7 GPa. The shape of a spherical Fermi surface with humps along &lt;111&gt; changes slightly at 2.5 GPa. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.11.200

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The DC magnetization of insulating UO2 under high pressure up to similar to 1 GPa has been measured using a piston-cylinder cell. Pressure-induced weak ferromagnetism was found to appear at low pressure (similar to 0.2 GPa). Both the remanent magnetization and the coercive force increase as pressure increases. This weak ferromagnetism may come from spin canting or from uncompensated moments around grain boundaries. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.11.307

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The magnetic properties of molecular oxygen adsorbed in the micro-porous metal-organic solids have been investigated. Adsorbed O-2 molecules form a ladder structure in the nanochannels of CPL-1. The temperature dependence of susceptibility and the high-field magnetization process indicate the nonmagnetic ground state of the adsorbed O-2 at low temperatures. (C) 2003 Elsevier B. V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.11.327

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We have carried out electrical resistivity rho and AC-susceptibility chi(AC) measurements on YbInCu4 under pressure. For pressures above 2.49 GPa, the first-order valence transition is completely suppressed and a clear peak appears in chi(AC) with a small kink in rho at T-M = 2.4 K. The chi(AC) peak is easily diminished by applying low magnetic fields and disappears above similar to 500 Oe. The characteristic behavior of chi(AC) at T-M can generally be ascribed to the onset of long-range ferromagnetic ordering and, therefore, the ground state of the pressure-stabilized phase of YbInCu4 is most probably a ferromagnetically ordered state. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jmmm.2003.11.146

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Language：English   Publisher：PHYSICAL SOC JAPAN  

We present recent advances in the magnetism and superconductivity of rare earth and uranium compounds. Heavy fermions are formed on the basis of the competition between the RKKY interaction and the Kondo effect in these compounds. The application of pressure to these compounds is useful to control the electronic states in the antiferromagnets CeRh2Si2 and CeRhIn5, and the ferromagnet UGe2. The quadrupole interaction or the quadrupole Kondo effect is found to be responsible for heavy fermions in PrFe4P12. A rich variety of superconducting properties are demonstrated: superconductivity of CeCoIn5 and CeRhIn5 in the vicinity of a quantum critical point, coexistence of ferromagnetism and superconductivity in UGe2, and superconductivity based on the quadrupole fluctuations in PrOs4Sb12, together with the relation between the superconducting transition temperature and the quasi-two dimensionality of the electronic states.

DOI： 10.1143/JPSJ.73.769

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：E D P SCIENCES  

The magnetization process of an S = 1/2 antiferromagnet on the Kagome lattice, [Cu-3(titmb)(2)(OCOCH3)(6)] . H2O{titmb = 1, 3, 5-tris(imidazol-1-ylmethyl)-2.4.6 trimethyl-benzene}, has been measured at very low temperature's in both pulsed and steady fields. We have found a new dynamical behavior in the magnetization process. A plateau at one third of the saturation magnetization M-s appears in the pulsed-field experiments for intermediate sweep rates of the magnetic field and disappears in the steady-field experiment's. A theoretical analysis using exact diagonalization yields J(1) = 19+/-2 K and J(2) = 6+/-2 K. for the nearest-neighbor and second-nearest-neighbor interactions. respectively. This set of exchange parameters explains the very low saturation field and the absence of the plateau in the thermodynamic equilibrium as well as the two-peak feature in the magnetic heat. capacity observed by Honda et. al. (Z. Honda et al., J. Phys. Condens. Matter. 14 (2002) L625). Supported by numerical results we argue that a dynamical order by disorder phenomenon could explain the transient appearance of the M-s/3 plateau in pulsed-field experiments.

DOI： 10.1209/epl/i2003-10164-5

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP PUBLISHING LTD  

The Knight shift K and the nuclear spin-lattice relaxation time T-1 of Li-7 have been measured under high pressure up to 4.74 GPa. 1/T1T becomes larger on applying higher pressure below 10 K and does not obey the T1T = constant relation down to 1 K. Meanwhile, K is independent of pressure above 2 GPa, indicating that the uniform component of the susceptibility does not change under high pressure. These results indicate that some antiferromagnetic fluctuations with wavevector q not equal 0 dominate the relaxation rate in LiV2O4 near the boundary of the pressure induced insulating phase. It is noted that the pressure dependence of T-1 for LiV2O4 is opposite to that of typical Ce HF compounds, such as CeCu5.9Au0.1 and CeCu2Si2. At the highest pressure of 4.74 GPa, we found that 1/T-1 obeys a power law dependence of T-2/3 over the wide T range between 60 mK and 10 K. The spin dynamics under high pressure will be discussed.

DOI： 10.1088/0953-8984/16/11/007

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We have succeeded in growing a single crystal of CeNiIn4 with the orthorhombic crystal structure by the In-flux method. CeNiIn4 is found to order antiferromagnetically below 1.4 K, with a successive change of the magnetic structure below 0.75 K. The magnetic phase diagram was formed by the specific heat and magnetization measurements. The electronic specific heat coefficient is determined as 80 mJ/ K(2.)mol. From these experimental results it is concluded that CeNiIn4 is a usual 4f-localized compound.

DOI： 10.1143/JPSJ.73.664

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We report the discovery of pressure-induced superconductivity in ferromagnetic UIr, which lacks inversion symmetry in the crystal structure. The Curie temperature T-CI = 46 K at ambient pressure decreases with increasing pressure, reaching a value of 11 K at 1.5 GPa. It presumably decreases further up to about P-cl = 1.7 GPa. The ferromagnetic region named 'Fl' exists up to P-cl. A second magnetic phase named 'F2' with a low ferromagnetic moment appears in the pressure range frorn 1.9 to 2.4 GPa. In the 'F2' phase, the magnetic transition temperature T-C2 decreases with pressure, from 18 K at 1.9 GPa to approximately zero at P-C2 = 2.6-2.7 GPa. In this critical pressure region, superconductivity appears below T-sc = 0.14 K.

DOI： 10.1088/0953-8984/16/4/L02

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We report similarities and differences of the transport features in the spin density wave (SDW) and in the field-induced SDW (FISDW) phases of the quasi-one-dimensional compound (TMTSF)"2PF"6. As temperature decreases below ≈2 K, the resistance in both phases exhibits a maximum and a subsequent strong drop. However, the characteristic temperature of the R(T) maximum and its scaling behavior in different magnetic fields B are evidence that the nonmonotonic R(T) dependences have different origin in SDW and FISDW regions of the phase diagram. We also found that the borderline T"0(B, P) which divides the FISDW region of the P-B-T phase diagram into the hysteresis and nonhysteresis domains terminates in the N = 1 subphase; the borderline thus has no extension to the SDW N = 0 phase. © 2004 MAIK "Nauka/Interperiodica".

DOI： 10.1134/1.1862799

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We have measured the electrical resistivity of an antiferromagnetic Kondo compound CeNiGe3 under pressure. The Néel temperature initially increases with pressure P up to 3 GPa, then decreases rather steeply with further increasing pressure, and becomes zero at a critical pressure P c ≃ 5.5 GPa. The A and ρ0 values of the resistivity ρ0 + AT2 in the Fermi liquid relation become maximum around P c, the A value attaining an extremely large value which is comparable with that in a heavy fermion superconductor CeCu2Si2. Superconductivity is found below 0.48 K in a wide pressure region from 4 to 10 GPa. The upper critical field Hc2(0) is about 2 T, indicating heavy fermion superconductivity.

DOI： 10.1088/0953-8984/16/20/L01

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Language：Japanese   Publisher：The Japan Society of High Pressure Science and Technology  

We have developed high-pressure NMR technique with an Indenter Cell using NiCrAl alloy. It was designed to set easily into a conventional dilution fridge and/or high field magnet. We have succeeded in ⁷Li-NMR measurement of a heavy fermion spinel LiV₂O₄ in T-range between 60 mK and 30 K under pressure up to 4.7 GPa. At ambient pressure, 1/T₁ shows a broad maximum around 50 K and is proportional to the temperature below 6 K. This is quite similar to the relaxation behavior in f-electron HF systems. However, 1/T₁T becomes larger with applying higher pressure below 10 K and does not obey T₁T = constant relation down to 1 K. Knight shift K, meanwhile, is independent of pressure above 2 GPa, indicating that the uniform component of susceptibility χ(0) does not change under high pressure. Some antiferromagnetic fluctuations with wave vector q ≠ 0 dominate relaxation rate in LiV₂O₄ near the boundary of the pressure induced insulating phase.

DOI： 10.4131/jshpreview.13.314

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A series of the ternary compounds CeTBi2 (T: Ni, Cu and Ag) have been grown in the single crystalline form by means of the flux method. These compounds crystallize in the tetragonal crystal structure. Measurements of the electrical resistivity, magnetic susceptibility, magnetization, low temperature specific heat and de Haas-van Alphen effect are reported. These compounds order antiferromagnetically with an easy-axis of magnetization along the [001] direction(c-axis). The electrical resistivity and magnetic susceptibility are highly anisotropic, reflecting the quasi-two dimensional crystal structure.

DOI： 10.1143/JPSJ.72.2632

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We have succeeded in growing a single crystal of CePtGe2 with the orthorhombic crystal structure by the Bi-flux method. In order to investigate the anisotropic properties, the magnetic susceptibility, magnetization and electrical resistivity measurements have been performed along the principal axes. From these measurements, it is found that CePtGe2 orders ferromagnetically below T-C = 5.1 K, and the magnetic easy-axis corresponds to the a-axis. The anisotropic properties have been analyzed on the basis of the crystalline electric field model. We have also studied the pressure effect on the ferromagnetic ordering, and T-C is found to increase with increasing pressure. However, T-C smears out around 3.5 GPa and a new phase appears at higher pressures, where the transition temperature of the new phase also increases with increasing pressure.

DOI： 10.1143/JPSJ.72.2338

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The do magnetization of insulating UO2 under high pressure up to similar to 1 GPa has been measured using a piston-cylinder cell. Pressure-induced weak ferromagnetism appeared at low pressure (similar to0.2 GPa). Both the remanent magnetization and the coercive force increase as pressure increases. This weak ferromagnetism may come from spin canting or from uncompensated moments around grain boundaries.

DOI： 10.1088/0953-8984/15/28/321

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We have measured the electrical resistivity under pressure up to 2 GPa for an antiferromagnet, CeRhGe. The resistivity at ambient pressure decreases monotonically below a Neel temperature T-N = 10 K. With increasing pressure P, the resistivity has a peak around 10 K, which is anomalously enhanced up to 1.2 GPa. With further increasing pressure, the resistivity peak is diminished; the Neel temperature becomes zero at a critical pressure P-c = 9 GPa. The A-value of the resistivity rho in the Fermi liquid relation rho = rho(0) +AT(2) is also found to increase with increasing pressure and has a maximum at Pc which corresponds to the value for the heavy-fermion superconductor CeCu2Si2.

DOI： 10.1088/0953-8984/15/29/102

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We present a theoretical and experimental study of a quasi-one-dimensional zigzag antiferromagnet (N2H5)CuCl3, which can be viewed as weakly coupled Heisenberg chains with a frustrated interaction. We first discuss generic features of the magnetic properties of the zigzag spin chain between the nearly single chain case and the nearly double chain case, on the basis of the finite temperature density-matrix renormalization group (DMRG) calculations. We next show the experimental results for the magnetic susceptibility and the high-field magnetization of a single crystal of (N2H5)CuCl3 above the Neel temperature T-N = 1.55 K. By comparing the experimental data with the DMRG results carefully, we finally obtain the ratio of the nearest and next-nearest exchange couplings as J(1)/J(2) = 0.25 with J(2)/k(B) = 16.3 K. We also investigate the three-dimensional (3D) coupling J' effect by using mean-field theory combined with the DMRG calculations. The estimated value J' similar to 0.04J(2) supports the one-dimensionality of (N2H5)CuCl3 above T-N.

DOI： 10.1088/0953-8984/15/21/309

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When pressure is applied to cerium and uranium compounds, the magnetic ordering temperature is suppressed and becomes zero at a critical pressure P-c. Around P-c, non-Fermi liquid and/or superconductivity are observed. We clarified a change of the electronic state via a de Haas-van Alphen (dHvA) experiment when pressure crosses P-c. The dHvA experiment under pressure was done for the antiferromagnets CeRh2Si2 and CeRhIn5, and for a ferromagnet UGe2. We found an abrupt change of the Fermi surface for CeRh2Si2 and UGe2 when crossing P-c, indicating a first-order like phase transition. For CeRhIn5, the topology of the Fermi surface was unchanged, but the cyclotron mass increased steeply above 1.6 Gpa, where superconductivity sets in. (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(03)00070-2

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To elucidate the ground state of the pressure-stabilized high-temperature (HT) phase of YbInCu4, we have carried out electrical resistivity rho and ac-susceptibility chi(ac) measurements at high pressures. For pressures above 2.49 GPa, the first-order valence transition is completely suppressed (below similar to80 mK). Separately, above 2.39 GPa, a clear peak appears in chi(ac) with a small kink in rho at around T-M=2.4 K. The chi(ac) peak is easily diminished by applying low magnetic fields and disappears above similar to500 Oe. The characteristic behavior of chi(ac) at T-M can generally be ascribed to the onset of long-range ferromagnetic ordering and, therefore, the ground state of the pressure-stabilized HT phase is most probably a ferromagnetically ordered state. This result is compatible with the occurrence of weak ferromagnetism recently reported for the Y-substituted compound Yb0.8Y0.2InCu4 under pressure of 1.2 GPa.

DOI： 10.1103/PhysRevB.67.224409

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We performed the heat capacity, C(T), measurement under high pressure on a ferromagnetic superconductor UGe2, in order to study the pressure dependence of the anomaly in C(T) associated with the superconducting transition. A clear peak appears only around a critical pressure P-c(*) where an another transition temperature T* becomes 0 K. This result suggests that a bulk superconducting phase exists in the narrower pressure region around P-c(*), than those clarified by previous studies. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4534(02)02650-3

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We report the results of specific heat measurements in a magnetic field on single crystal samples of the S = 1 quasi-1D bond alternating antiferromagnet Ni(C9H24N4)NO2(ClO4). The compound has the singlet ground state with an excitation energy gap and the gap closes by application of magnetic field (H-c). We observed a sharp peak corresponding to the long-range ordering above Hc both parallel and perpendicular to the chain at low temperatures. The temperature-magnetic field phase diagram is discussed in comparison with those of the Haldane system Ni(C5H14N2)(2)N-3(PF6). (C) 2003 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(02)02130-0

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ACTA PHYSICA POLONICA B, JAGELLONIAN UNIV, INST PHYSICS  

We performed the heat capacity, C(T), measurement under high pressure for a ferromagnetic superconductor UGe2. At 1.15 GPa, we found a peak in C/T at a characteristic temperature, T-* = 6 K where the magnetization showed anomalous increase. At 1.28 GPa, above the critical pressure P-c(*) where T-* becomes 0 K, C/T does not show notable anomaly at zero magnetic field, but the application of the external field above 2.5 T induces the peak again at T-* &gt; 0 K. It corresponds to the induction of T-* by the magnetic field. Our experimental result suggests that a second order phase transition takes place at T-* and thus a disappearance of the phase transition at T-* is of second order.

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When pressure is applied to the cerium and uranium compounds, their magnetic ordering temperatures are suppressed and become zero at a critical pressure P-c. Around P-c non-Fermi liquid and/or superconductivity are observed. We clarified a change of the electronic state via the de Haas-van Alphen (dHvA) experiment when pressure crosses P-c. The dHvA experiment under pressure was done for antiferromagnets CeRh2Si2, CeRhIn5 and URu2Si2, and a ferromagnet UGe2. We find an abrupt change of the Fermi surface for CeRh2Si2 and UGe2 when crossing P-c, indicating a first-order like phase transition. For CeRhIn5 and URu2Si2, a change of the cyclotron mass is clearly observed.

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We have studied the effect of pressure on the electrical resistivity of a high-quality single crystal CeAgSb2 which has a small net ferromagnetic moment of 0.4 mu(B)/Ce. The magnetic ordering temperature. T-ord = 9.7 K decreases with increasing pressure p and disappears at a critical pressure p(c) similar or equal to 3.3 GPa. The residual resistivity, which is close to zero up to 3 GPa, increases steeply above 3 GPa, reaching 55 muOmega cm at p(c). A huge residual resistivity is found to appear when the magnetic order disappears.

DOI： 10.1088/0953-8984/15/4/101

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DOI： 10.1016/S0921-4534(02)02731-4

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Evolution of the pressure-induced heavy fermion state and superconductivity in CeRhIn5 have been established by high-pressure Fermi surface studies using dHvA technique. The effective mass of the conduction electrons named branch beta(2) increases from 5.5 m(0) at ambient pressure to 20 m(0) at 1.6 GPa where superconductivity sets in. This heavy electron mass continues to increase steeply up to 2.1 GPa, 45 m(0) at 2.1 GPa, with a concomitant increase of the superconducting transition temperature. However, the underlying Fermi surface remains approximately same even at 2.1 GPa, strongly suggesting that antiferromagnetic fluctuations of Ce moments do not contribute to the volume of the Fermi surface, but enhance the cyclotron mass of the conduction electrons.

DOI： 10.1103/PhysRevB.66.214510

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We report the direct observation of dioxygen molecules physisorbed in the nanochannels of a microporous copper coordination polymer by the MEM (maximum entropy method)/Rietveld method, using in situ high-resolution synchrotron x-ray powder diffraction measurements. The obtained MEM electron density revealed that van der Waals dimers of physisorbed O(2) locate in the middle of nanochannels and form a one-dimensional ladder structure aligned to the host channel structure. The observed O-O stretching Raman band and magnetic susceptibilities are characteristic of the confined O(2) molecules in one-dimensional nanochannels of CPL-1 (coordination polymer 1 with pillared layer structure).

DOI： 10.1126/science.1078481

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Electrical resistivity measurements in a magnetic field are carried out on UGe2 which exhibits pressure-induced superconductivity. The superconductivity is observed from 1.06 to 1.44 GPa. In the temperature and field dependences of the resistivity at P &gt; PC where the ferromagnetic ordering disappears, it is observed that the application of an external field along the a-axis increases the coefficient A of the Fermi-liquid behaviour (alphaAT(2)) abruptly-corresponding to the metamagnetic transition. The characteristic enhancement of H-C2 is reconfirmed for H parallel to a-axis. The upper critical field of H-C2 is anisotropic: H-C2(T) exhibits positive curvature for H parallel to b-axis and H parallel to c-axis.

DOI： 10.1088/0953-8984/13/1/103

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We carried out the de Haas-van Alphen (dHvA) experiment under pressure to clarify the nature of f-electron compounds of CeRh2Si2, UGe2 and CeCoIn5. With increasing pressure, the Neel temperature T-N = 36 K in CeRh2Si2 and the Curie temperature T-C = 52 K in UGe2 decrease, and a quantum critical point corresponding to the extrapolation T-N or T-C --&gt; 0 is reached at the critical pressure p(c) similar or equal to 1.06 and 1.52 GPa, respectively. Experimental results indicate a discontinuous change of the Fermi surface in CeRh2Si2 and UGe2 when the pressure crosses pc. A heavy fermion superconductor CeCoIn5 with a quasi-two dimensional Fermi surface was found to be located in the vicinity of the quantum critical point. (C) 2002 Elsevier Science Ltd. All rights reserved.

DOI： 10.1016/S0022-3697(02)00156-7

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We studied the pressure effect by measuring the electrical resistivity for a high-quality single crystal of an antiferromagnet CeRh2Si2 with the tetragonal structure. The Neel temperature becomes zero around I GPa. An onset of superconductivity appears below 0.5 K in a relatively wide pressure region from 0.97 to 1.20 GPa, while the resistivity zero, which appears below 0.4 K, is found to be located in an extremely narrow region from 1.03 to 1.08 GPa. Correspondingly the A value of the Fermi liquid relation in the electrical resistivity (rho = rho(0) + AT(2)) becomes maximum around I GPa. Superconductivity is realized in a heavy fermion state.

DOI： 10.1088/0953-8984/14/21/102

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We have studied the effect of pressure on the electrical resistivity of the antiferrornagnet CeMg2Cu9 which crystallizes in the hexagonal structure. The structure is built up of alternating MgCu2 Laves-type and CeCu5-type layers along the [0001] direction. The Neel temperature T-N = 2.7 K at ambient pressure decreases with increasing pressure p and disappears at a critical pressure p(e) similar or equal to 2.5 GPa. Correspondingly, the residual resistivity rho(0) and the coefficient A in a Fermi-liquid relation rho = rho(0) + AT(2) are found to have maximum values around p(e).

DOI： 10.1088/0953-8984/14/14/101

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Recently, co-existence of the ferromagnetism and superconductivity was reported in the high-pressure region (1.0-1.6 GPa) in UGe2. We performed the heat capacity measurement on UGe2 under high pressure. At 1.15 GPa, we found a peak corresponding to the superconducting transition. The superconducting temperature T-sc and DeltaC/(gammaTSC) are 0.6 K and 0.25, respectively. The superconducting transition was also confirmed by the appearance of the Meissner effect in the AC susceptibility. From these results, we confirm a bulk nature of the superconductivity in UGe2. The value of C/T (similar to 95 mJ/molK(2)) just above Tsc at 1.15 GPa is as much as 3 times larger than that at ambient pressure, which indicates a large mass enhancement of quasiparticles under high pressure. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(01)01076-6

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Transport properties of a pressure-induced superconductor CeRhIn5 were investigated under high pressures up to 8.5 GPa by using a diamond-anvil cell. Superconductivity was observed in a wide pressure range from 1.5 to 7.6 GPa.We also investigated the transport properties in the external magnetic field in order to study a characteristic temperature dependence of the resistivity in the normal state. (C) 2002 Published by Elsevier Science B.V.

DOI： 10.1016/S0921-4526(01)01091-2

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The nuclear spin lattice relaxation time (T-1) Li-7 in the heavy fermion system LiV2O4 has been measured under high pressure up to 3.7 GPa. At ambient pressure, 1/T-1 shows broad maximum around 50K and is proportional to the temperature below 8 K. This is apparently quite similar to the relaxation behavior in f-electron systems. However, 1/T-1 becomes larger with applying higher pressure below 10 K and does not obey T1T =constant relation down to I K. This pressure dependence of T, is opposite to that of Cc compounds, such as CeCu5.9Au0.1 and CeCu2Si2. Spin dynamics of LiV2O4 under pressure is discussed. (C) 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(01)01492-2

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Magnetoresistance measurements on the quasi-one-dimensional organic conductor (TMTSF)2PF6 performed in magnetic fields B up to 16 T, temperatures T down to 0.12 K and under pressures P up to 14 kbar have revealed new phases on its P-B-T phase diagram. We found a new boundary which subdivides the field induced spin density wave (FISDW) phase diagram into two regions. Whereas a low-temperature region of the FISDW diagram is characterized by a hysteresis behavior typical for the first-order transitions, in a hightemperature region of the FISDW phase diagram, the hysteresis was found to disappear. We also found that the temperature dependence of the resistance (at a constant B) changes sign at about the same boundary. We compare these results with recent theoretical models.

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We have performed the de Haas-van Alphen (dHvA) and ac-susceptibility experiments on a ferromagnet UGe2 under pressure for the field along the easy a-axis. The p-H phase diagram was determined, indicating three kinds of phase: paramagnetic and weakly and strongly polarized phases. The detected dHvA frequencies as well as the cyclotron masses are found to be very different between the weakly and strongly polarized states. A change of the Fermi surface occurs when the weakly polarized phase is changed into the strongly polarized phase with increasing magnetic field.

DOI： 10.1088/0953-8984/14/5/103

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Magnetoresistance measurements on the quasi-one-dimensional organic conductor (TMTSF)(2)PF6 performed in magnetic fields B up to 16 T, temperatures T down to 0.12 K and under pressures P up to 14 kbar have revealed new phases on its P-B-T phase diagram. We found a new boundary which subdivides the field induced spin density wave (FISDW) phase diagram into two regions. Whereas a low-temperature region of the FISDW diagram is characterized by a hysteresis behavior typical for the first-order transitions, in a high-temperature region of the FISDW phase diagram, the hysteresis was found to disappear. We also found that the temperature dependence of the resistance (at a constant B) changes sign at about the same boundary, We compare these results with recent theoretical models.

DOI： 10.1103/PhysRevB.65.060404

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We report the pressure (P)-temperature (T) phase diagram of antiferromagnetism and superconductivity in CeRhIn5 and CeIn3 revealed by the 115In nuclear-spin-lattice-relaxation (T1) measurement. In the itinerant magnet CeRhIn5, we found that the Néel temperature TN is reduced at P ≥ 1.23 GPa with an emergent pseudogap behavior. In CeIn3, the localized magnetic character is robust against the application of pressure up to P ∼ 1.9 GPa, beyond which the system evolves into an itinerant regime in which the resistive superconducting phase emerges. We discuss the relationship between the phase diagram and the magnetic fluctuations.

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We carried out the de Haas-van Alphen (dHvA) experiment under pressure for a ferromagnet UGe2. The dHvA frequency of a main dHvA branch named a, that corresponds to a majority up-spin band 40-hole Fermi surface, decreases monotonously with increasing pressure, but in the pressure range from p(c)* (similar or equal to1.2 GPa) to p(c) (similar or equal to1.5 GPa) the dHvA signal disappears completely, where p(c) and p(c)* correspond to critical pressures for a Curie temperature T-C and the C second phase transition temperature T* (&lt;T-C), respectively. For p &gt; p(c) we observed new dHvA branches with large cyclotron masses of 19-64m(0), which correspond to main Fermi surfaces in the paramagnetic state.

DOI： 10.1088/0953-8984/14/1/104

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We have studied Fermi surface properties of LaRhIn5 and CeTIa(5) (T: Co, Rh and Ir) via the de Haasvan Alphen (dHvA) experiment. The Fermi surface of a non-4f reference compound LaRhIn5 is quasi-two dimensional, reflecting the unique tetragonal crystal structure, which is consistent with the result of FLAWP energy band calculations. The Fermi surface of an antiferromagnet CeRhIn5 is similar to that of LaRhIn5 although the cyclotron mass in CeRhIn5 is roughly by one order larger than that in LaRhIn5. Both Fermi surfaces are. however, different from those of CeCoIn5 and CcIrIn(5) which are well explained by the 4f-itinerant band model. The 4f electrons in CeRhIn5 thus do not contribute to the volume of ate Fermi surface. We have also studied magnetic and superconducting properties of CeCoIn5 and CeIrIn5.

DOI： 10.1143/JPSJ.71.162

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We report the pressure (P)-temperature (T) phase diagram of antiferromagnetism and superconductivity in CeRhIn5 and CeIn3 revealed by the In-115 nuclear-spin-lattice-relaxation (T-1) measurement. In the itinerant magnet CeRhIn5, we found that the Neel temperature T-N is reduced at P greater than or equal to 1.23 GPa with an emergent pseudogap behavior. In CeIn3, the localized magnetic character is robust against the application of pressure up to Psimilar to1.9 GPa, beyond which the system evolves into an itinerant regime in which the resistive superconducting phase emerges. We discuss the relationship between the phase diagram and the magnetic fluctuations.

DOI： 10.1103/PhysRevB.65.020504

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Low-temperature specific heat and its field-dependence up to 16 T was measured in a stoichiometric single crystal of YbP. A sharp peak was observed at $T_{\text{N } } = 0.53$ K in zero magnetic field. Application of external field seems to induce a new magnetic phase above 11 T. The field dependence of the transition temperature in the high-field phase is different from that of the low field phase. The linear coefficient of the electronic specific heat is estimated as 120 mJ/mol$\cdot$K2 from low temperature specfic heat, suggesting heavy Fermion state in YbP.

DOI： 10.1143/JPSJ.71.1365

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Thermal properties of a ferromagnetic superconductor UGe2 were investigated by the heat capacity measurements. The bulk nature of the superconductivity was confimied by the observation of a peak in the heat capacity at the superconducting transition temperature T SC, From the pressure dependence of the linear heat capacity coefficient γ, it is suggested that the low energy magnetic excitation near the critical point Pc*, where T* becomes OK, might play an important role on the superconductivity. The pressure dependence of the superconducting peak and the temperature dependence of CIT above T SC suggest that the order parameter of the superconducting state might be different between the phases below and above PC *. © 2002 Atomic Energy Society of Japan. All rights reserved.

DOI： 10.1080/00223131.2002.10875442

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The transport properties of the itinerant ferromagnet U3P4 have been studied at high pressures up to 6.0 GPa using a diamond anvil cell. The Curie temperature TC decreases with increasing pressure, but then TC cannot be assigned above 4.0 GPa. The coefficient A, assuming the Fermi liquid behavior (p(T) = p0 + AT2) at low temperatures, shows a maximum at 5.3 GPa. The temperature dependence of the resistivity at 5.0 GPa follows T 5/3 which is expected in the SCR theory of a three dimensional ferromagnet. From these results, it is concluded that the ferromagnetic-nonmagnetic transition exists at around 5.0 GPa. © 2002 Atomic Energy Society of Japan. All rights reserved.

DOI： 10.1080/00223131.2002.10875441

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The magnetic behavior of the nickel cubane complex [Ni-4(OMe)(4)(sal)(4)(MeOH)(4)] (Hsal = salicylaldehyde) was studied by using a Hartshorn bridge equipped with a He-3/He-4 dilution refrigerator. This complex has long been known to have a well-isolated high-spin ground state with S = 4 and it was suggested to have an easy-axis type anisotropy. AC magnetic susceptibility data clearly show a slow magnetization reversal below 0.3 K, characteristic of single-molecule magnets. The Arrhenius plot of the relaxation rate provides the activation energy of about 5 K.

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Evolution of the pressure-induced heavy fermion state and superconductivity in (formula presented) have been established by high-pressure Fermi surface studies using dHvA technique. The effective mass of the conduction electrons named branch (formula presented) increases from 5.5 (formula presented) at ambient pressure to 20 (formula presented) at 1.6 GPa where superconductivity sets in. This heavy electron mass continues to increase steeply up to 2.1 GPa, 45 (formula presented) at 2.1 GPa, with a concomitant increase of the superconducting transition temperature. However, the underlying Fermi surface remains approximately same even at 2.1 GPa, strongly suggesting that antiferromagnetic fluctuations of Ce moments do not contribute to the volume of the Fermi surface, but enhance the cyclotron mass of the conduction electrons. © 2002 The American Physical Society.

DOI： 10.1103/PhysRevB.66.214510

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

That the 4f electrons in the rare-earth antiferromagnetic compound CeRh2Si2 should be considered as localized electrons at cerium sites has been confirmed by comparing a de Haas-van Alphen experiment to the result of energy band calculations for LaRh2Si2. When pressure p is applied to the compound, the Neel temperature T-N1 = 36 K decreases and finally becomes zero at p(c)similar or equal to1.0-1.1 GPa. The topology of the Fermi surface is found to be almost unchanged up to 1.0 GPa, but the cyclotron effective mass increases with increasing pressure. Above 1.1 GPa, the topology of the Fermi surface changes abruptly. A new Fermi surface is explained by the 4f-itinerant-band model. The corresponding cyclotron mass is large, being about 22m(o).

DOI： 10.1103/PhysRevB.64.224417

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The pressure dependence of transport properties in CeRhIn5 was studied up to 8.5 GPa by using a diamond-anvil cell. The electrical resistivity does not follow the T-2-dependecne of a Fermi liquid nature under any pressure. In this non-Fermi liquid state, superconductivity was observed in a wide pressure range of 1.5 GPa &lt; P &lt; 7.6 GPa. The superconducting temperature TC has a double-maximum structure with a minimum at 5.2 GPa. A maximum of T-C = 2.2 K was observed at P = 2.5 GPa, where the corresponding electrical resistivity just above TC has the maximum. The upper critical field H-C2 and the magnetoresistances were also investigated under pressure.

DOI： 10.1143/JPSJ.70.3362

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We performed DC-magnetization and neutron scattering experiments under pressure P for a pressure-induced superconductor UGe2. We found that the magnetic moment is enhanced at a characteristic temperature T* in the ferromagnetic state, where T* is smaller than a Curie temperature T-C. This enhancement becomes remarkable in the vicinity of P-C* = 1.20 GPa, where T* becomes 0 K and the superconducting transition temperature T-SC shows a maximum. The characteristic temperature T*, which decreases with increasing pressure, also depends on the magnetic field.

DOI： 10.1143/JPSJ.70.2876

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DOI： 10.1088/0953-8984/13/1/103

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Neutron scattering experiments were carried out for the new Haldane compounds Ni(C5H14N2)(2)N-3(ClO4) (NDMAZ) and Ni(C5H14N2)(2)N-3(PF6) (NDMAP) in the magnetic field up to 10 T in order to investigate the field-induced long-range ordering and the spin excitation. For NDMAZ. the triplet excited state (1.61, 1.76, and 3.2 meV) and field dependence of these levels were observed at Q = (000.5). From these data. the intra-chain coupling constant approximate to 4.3 meV and the anisotropic parameters D approximate to 0.76 meV and /E/ approximate to 0.038 meV were estimated. For NDMAP the gap was observed at about 0.48 and 0.64 meV at Q (000.5). By applying the field of 5 T, the first excited state shifted below the resolution less than 0.13 meV. Above the critical field H-C, the intensities of singlet-triplet excitation becomes very weak. This work is the first neutron scattering study on a Haldane system above the critical fields. (C) 2001 Elsevier Science B.V. All rights reserved.

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Appearance of the field-induced long-range ordering was observed directly by a proton NMR measurement in Haldane gap system, Ni(C5H14N2)(2)N-3(PF6) (NDMAP). A sudden splitting of the spectrum due to the appearance of the transverse staggered moment was observed just below T-N. The transverse staggered moment is estimated as 1.1 mu (B) in the external field of 10.9 T parallel to the ab-plane. (C) 2001 Elsevier Science B.V. All rights reserved.

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Field-induced long-range ordering is investigated by heat capacity and high-field magnetization measurements in Haldane gap system Ni(C5H14N2)(2)N-3(ClO4) (NDMAZ). In the high-field magnetization measurement along the crystal c-axis, the differential magnetization is found to reveal the characteristic peak corresponding to the phase transition to the ordered state. The magnetization increases as (H - H-C)(0.6) at the lowest temperature. The phase boundary determined down to 44 mK by the peak of the differential magnetization obeys T-N similar to (H - H-C)(0.45). Anisotropic phase diagram is similar to that of Ni(C5H14N2)(2)N-3(PF6) (NDMAP).

DOI： 10.1143/JPSJ.70.813

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The temperature dependence of the magnetic susceptibility and the high-field magnetization up to 55T are measured for URu2Si2 under high pressures up to 1 GPa. Both T-chi max and T-N in the susceptibility increase with increasing pressure. The Value of the susceptibility below T-chi max decreases with increasing pressure. The three high-held metamagnetic transitions at H-c1 = 35.1T, H-c2 = 36.5 T and H-c3 = 39.6 T at ambient pressure, show different pressure-dependent behaviors. The metamagnetic transition at H-c1 broadens but survives and its transition field increases with increasing pressure. However, the transition at H-c2 is smeared out and disappears above 0.4 GPa. The transition at H-c3 broadens more clearly than the transition at H-c1. The fact that both T-chi max and the metamagnetic transition fields increase suggests that the interaction between the f-electrons and the conduction electrons is enhanced by pressure. (C) 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(00)00657-8

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We confirmed bulk-superconductivity of a ferromagnet UGe2 by the specific heat measurement, together with the measurements of the electrical resistivity and ac susceptibility, in a pressure range from p = 1.0 to 1.5 GPa, where the Curie temperature T-C(= 22-36 K) is still high, but another characteristic temperature T* is close to zero. In this pressure range, the heavy fermion state is found to be formed at low temperatures.

DOI： 10.1088/0953-8984/13/1/103

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We succeeded in growing a high-quality single crystal of CeRh2Si2 with a residual resistivity ratio of 110. Under a pressure of 1.1 GPa, superconductivity is found below Tc = 0.38 K, where a Néel temperature of TN = 36K is suppressed down to almost zero. © 2001 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(00)00785-X

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Neutron scattering experiments were carried out in order to investigate the field-induced. antiferromagnetic long-range order and spin dynamics for the new Haldane compounds Ni(C5H14N2)(2)N-3 (ClO4) (NDMAZ) and Ni(C5H14N2)(2)N-3 (PF6) (NDMAP). We observed the energy gaps corresponding to the excited triplet, Delta (chi) = 1.61 meV, Delta (gamma) = 1.76 meV, Delta (z) = 3.2 meV for NDMAZ and Delta (chi), = 0.48 meV, Delta (gamma), = 0.64 meV for NDMAP. The dispersion in NDMAZ was well explained by the theoretical curve with the intra-chain interaction J = 50 K. The field dependence of the gap energy below critical field (H-c), was observed for NDMAZ and NDMAP as applying the field perpendicular to the chain direction. The field dependence of the excitation levels in NDMAZ was well explained by the fermionic field-theory treatment of the one-dimensional Heisenberg antiferromagnetic Hamiltonian with these gap energies and g-value, 2.3. In NDMAP, we found that the excitation peaks at Q = (0 0 0.5) became unobservably weak above H-c. This result would indicate a level crossing between the ground and the excited level at H-c and the change of the ground state above H-c. No trace of the magnetic Bragg peak due to the field induced ordering could be observed in the present study with our non-deuterated single crystal sample.

DOI： 10.1143/JPSJ.69.4034

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Specific heat and effect of pressure on the electrical resistivity of CePtGa single crystal have been measured upto 30 kbar. A sharp peak in the ratio of specific heat to temperature and in electrical resistivity is observed at 33 and 3.5 K, respectively, which is ascribed to an antiferromagnetic transition. The results reveal that T-N decreases linearly with increasing pressure upto 30 kbar. (C) 2000 Elsevier Science B.V. All rights reserved.

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Pressure dependence of electrical resistance in CeB6 is investigated up to 13 GPa. A maximum in temperature dependence of the resistance shifts to higher temperature by the application of pressure. The quadrupole ordering temperature T-Q shows no obvious pressure dependence at zero field, while the field dependence of T-Q is enhanced slightly under high pressure. (C) 2000 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(99)00947-3

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High-field magnetization measurements in a heavy fermion antiferromagnet CeRh2Si2 were performed under high pressures at various temperatures to study the nature of the metamagnetism. Metamagnetic transitions were observed not only in the antiferromagnetic state but also in the paramagnetic stale at various pressures, The metamagnetism in CeRh2Si2 does not originate from the rearrangement of antiferromagnetic moments but from the recovery of the local moment from the Kondo singlet state by applying high magnetic fields. (C) 2000 Published by Elsevier Science B.V. All rights reserved.

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Electrical resistance has been investigated in a high-quality polycrystal of CeRh2Si2 under high pressures of up to 5.4 GPa. We found a resistance drop corresponding to superconductivity in the pressure range from 0.7 to 2.9 GPa. The relative decrease of the resistance shows a maximum in the vicinity of a critical pressure Pc. An onset temperature of superconductivity is about 0.6 K. (C) 2000 Elsevier Science B.V. All rights reserved.

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The alternating one-dimensional Heisenberg S = 1/2 chain compound with spin gap, (VO)(2)P2O7, has been studied by the high-field magnetization and P-31 NMR measurements. Two critical phenomena at 25 +/- 1 and 46 +/- 2 T are observed in the magnetization curve, which are considered to be a crossover between the ground state and the excited state in two kinds of gap systems. P-31 NMR also revealed the coexistence of two magnetic systems with independent spin gaps. Results obtained from the present and previous studies are well explained by the model in which two kinds of magnetic chains along the b axis behave as alternating spin chains with independent gap energies.

DOI： 10.1103/PhysRevLett.83.3729

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The heat capacity and magnetization measurements of the single crystal of Haldane-gap antiferromagnet NDMAZ were carried out at low temperatures down to 0.1 K and under magnetic fields up to 14 T. We have observed three-dimensional long-range ordering of NDMAZ at around T similar or equal to 0.3 K above H similar or equal to 13 T (H parallel to c), which is ascribed to both the field-induced gap quenching and the existence of finite interchain interaction. Applying the higher external held, the transition temperature reaches up to 0.6 K at H = 14 T, showing a negative curvature with respect to the external field. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0304-8853(98)00804-X

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Magnetic and transport properties have been investigated in the single crystal of CeRh2Si2 under high pressures. We found that the magnetic susceptibility under high pressure shows a broad maximum like CeRu2Si2. In the present pressure range up to 13 kbar where the ordered state is suppressed, no obvious evidence of the superconducting transition is observed down to 50 mK. (C) 1999 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0921-4526(98)00909-0

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The pressure range for electrical transport measurements has been dramatically increased up to 220 GPa in the 0.05-300 K temperature region and at magnetic fields of up to 10 T. Metallization of caesium iodide was found at a pressure of 115 GPa. A superconducting transition with T c = 2 K was observed above 180 GPa. T c decreases with increasing pressure. The superconducting transition shifts to lower temperatures and disappears under magnetic field above 0.3 Tesla.

DOI： 10.1088/0953-8984/10/49/037

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A review of recent developments in high-pressure techniques and their application in the search for superconductivity at low temperature is presented. We have focused the discussion mainly on the experimental results obtained by our group for simple molecular systems.

DOI： 10.1088/0953-8984/10/49/008

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Language：English   Publisher：The Physical Society of Japan (JPS)  

From the 7Li nuclear magnetic resonance (NMR) and specific heatmeasurements of LiNiO2, consisting of a spin-1/2 triangular lattice, itis demonstrated that the previously suggested spin-glass-like freezingbelow Tsg=8 K, which is caused by defects of Li ions, is not the trueground state, but rather a quantum disordered state is realized without aspin gap. This state is characterized by power-law behavior of thetemperature dependence of the specific heat below 0.5 K. A spin-liquidstate with short-range ferromagnetic correlations is suggested from newinsight into the frustration of orbital ordering for doubly degenerateeg shells in the triangular lattice.

DOI： 10.1143/JPSJ.67.3703

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DOI： 10.1126/science.281.5381.1333

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Enhancement of superconducting transition temperature T c is confirmed at around 16 GPa in the pressure-induced superconductor CeCu2Ge2.The superconducting Hc-T c phase diagrams at the low-T c and high-T c pressure regions indicates that the heavy quasi particles form the singlet Cooper pairs.At both low-T c and high-T c pressure regions, Fermi liquid behavior of ρ∼ AT2 is observed only at low temperatures below 1 K in the normal state induced by the external field above Hc2.At 21 GPa where the superconductivity disappears down to 50 mK, the temperature region following ρ∼ AT2 increases drastically up to 40 K and the coefficient A decreases rapidly.These results indicate that the strongly correlated electrons are responsible essentially for the appearance of superconductivity in this system.

DOI： 10.1143/JPSJ.67.996

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：American Physical Society  

DOI： 10.1103/PhysRevB.57.5025

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DOI： 10.1016/S0921-4526(98)00023-4

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Magnetic properties of oxygen physisorbed in Cu-trans-1,4-cyclohexanedicarboxylic acid having one-dimensional micropores are studied. O-2 is well known as a magnetic molecule with S=1. In the case of the low adsorption, temperature dependence of the susceptibility shows the Schottky-type broad peak and the high-field magnetization process has a step at around 34T with saturation moment of 2 mu(B)/O-2. These results are interpreted by the dimer model of S=1/2 with an antiferromagnetic exchange interaction. Broadening of the step of magnetization with increasing the adsorption may be due to the interdimer interaction or the distribution of the intra-dimer exchange interaction. Linear magnetization process which is characteristic of one-dimensional Heisenberg antiferromagnet has not been observed even in the full pore region.

DOI： 10.1080/10587259708044542

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We report the results of susceptibility and magnetization measurements on ferromagnetic-antiferromagnetic alternating chain compounds [Cu(TIM)]CuCl4 (TIM=2,3,9,10-tetramethyl-1,3,8,10-tetraenecyclo-1,4,8,11-tetraazatetradecane) and (4-BzpipdH)CuCl3 (4-BzpipdH=4-benzylpiperidinium). Magnetization curves of both compounds are compared to those calculated for an S=1 linear-chain Heisenberg antiferromagnet. From the fitting of susceptibility data to a numerical formula calculated for an S=1/2 ferromagnetic-antiferromagnetic alternating chain [Inog. Chem. 33 (1994) 5171], we have estimated theantiferromagnetic exchange constant J AF/k B=2.9 K, the ferromagnetic exchange constant |J F|/k B=4.7 K and the g-value of the magnetic moment g=2.06 for the former and J AF/k B=8.8 K, |J F|/k B=38.8 K and g=2.17 for the latter, which are different from the values reportedpreviously.

DOI： 10.1143/JPSJ.66.1792

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of High Pressure Science and Technology  

High-pressure cells which can be used in experiments at low temperatures and high magnetic fields are considered. New constructions of piston-cylinder, diamond anvil and other cells are presented. The recent development of a technique for resistance measurements in the megabar region above 150 GPa are presented. For the first time electrical measurements in the DAC with typical megabar anvils were performed with a sample of diameter 20 μm. The metallization of sulfur at 100 GPa, CsI at 120 GPa was achieved. Simultaneously, with electrical measurements the Raman spectra of sulfur were studied up to 100 GPa.

DOI： 10.4131/jshpreview.7.469

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：The Japan Society of High Pressure Science and Technology  

Experimental techniques on production of ultra-high pressure at very low temperature, electrical resistance and magnetization measurement are developed for the purpose of searching for pressure-induced superconductivity in some simple systems. Previous results of pressure induced superconductivity of I, Br, Ca, SnI₄ and C₆I₄O₂ are reviewed and remaining problems are discussed shortly. Recent findings of metallization and superconductivity of O and S are also reported.

DOI： 10.4131/jshpreview.7.688

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DOI： 10.1080/10587259708045083

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Magnetic susceptibilities of 5 kinds of 3-(4-R-phenyl)-1,5-dimethyl-6-oxoverdazyl radicals (PDOV (R=H), p-MDOV (R-CH3O), p-MeDOV (R=CH3), p-CyDOV (R=CN), and p-NDOV (R=NO2)) have been measured in the temperature range of 4.2-300 K. The susceptibilities of PDOV, p-MDOV, and p-MeDOV can be explained by an antiferromagnetic Heisenberg alternating chain model. The susceptibility of p-CyDOV shows a broad maximum at 54 K, and decreases abruptly at 15 K, suggesting a spin-Peierls transition, High-field magnetization data (H=0-35 T) which provide a clear evidence for a spin-Peierls transition were reported.

DOI： 10.1016/0009-2614(96)00577-5

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Electrical resistance of Ca is measured under pressures up to 150 GPa and at temperatures down to 0.05 K. Superconductivity is observed at temperatures below 3 K under pressures above 85 GPa. The superconducting transition temperature increases linearly with increasing pressure and reaches about 15 K at 150 GPa.

DOI： 10.1143/JPSJ.65.1924

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Effects of Cu-impurity are studied by heat capacity and susceptibility measurements down to 30 mK on the Haldane-gap antiferromagnet Ni(C2H8N2)2NO2(ClO4) (NENP). We have observed the characteristic heat capacity and susceptibility which show contributions from free spins of the Cu2+-impurities with S=1/2 and the fractional spin S=1/2 states at the ends of the Ni2+(S=1)-chain adjacent to the Cu2+-impurities. The present results are explained completely by the phenomenological Hamiltonian for a trimmer of S=1/2 proposed by the ESR study on this system.

DOI： 10.1143/JPSJ.64.2609

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Various types of ground states in strongly correlated electron systems have been systematically investigated by means of NMR/NQR at low temperatures under high magnetic field and pressure. We focus on two well-known heavy-electron families, CeCu2X2 (X = Si and Ge) (Ce(122)) and UM2Al3 (M = Ni and Pd) (U(123)). The Cu NQR experiments on CeCu2X2 under high pressure indicate that the physical property of CeCu2Ge2 at high pressure, i.e. above the transition at 7.6GPa from antiferromagnetic (AF) to superconductivity, are clearly related to that of CeCu2Si2 at ambient pressure. In addition to the H-T phase diagram established below 7 T, NMR and specific heat experiments on polycrystal CeCu2.05Si2 have revealed the presence of a new phase above 7 T. In a high-quality polycrystal of UPd2Al3 with a record high-T-c of 2 K at ambient pressure and the narrowest AI NQR line width, the nuclear-spin lattice relaxation rate, (27)(1/T-1) measured in zero field has been found to obey the T-3 law down to 0.13 K, giving strong evidence that the energy gap vanishes along lines on the Fermi surface. Thus it seems that all heavy-electron superconductors exhibit lines of zero gap, regardless of their different magnetic properties.

DOI： 10.1016/0921-4526(94)00365-3

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Heat capacity measurements of CeCu2.05Si2 have been carried out at temperatures down to 0.1 K under magnetic field up to 13 T. The heat capacity divided by temperature C/T has revealed as a characteristic feature that the peak of C/T shifts down to around 0.5 K with increasing field up to 7 T, whereafter it shifts up again to around 0.6 K at 13 T. In the first case, a peak appears around the phase boundary (labeled A) first found in NMR and magnetoresistance. Most remarkably, in the latter case, the peak coincides with the new phase boundary (labeled B) identified recently by elastic constant and thermal expansion measurements.

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Heat capacity and susceptibility measurements are performed downto 70 mK under magnetic fields in the Haldane-gap antiferromagnet(CH3)4NNi(NO2)3 (TMNIN). We have observedno magnetic long range order within our experimental range ofthe temperature down to 70 mK and the magnetic field up to7 T. The heat capacity reflects the field dependence of theenergy gap and show a broad anomaly above a critical fieldH C, which has been also observed in NENP. In theadiabatic magnetization measurement, the spin temperature showsa minimum around H C. These results are interpreted asincreasing of the energy gap above H C which maysuppress the expected long-range-ordering.

DOI： 10.1143/JPSJ.63.1961

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Heat capacity measurements of the quasi one-dimensional S=1 antiferromagnet Ni(C₂H₈N₂)₂NO₂(ClO₄) are performed in static magnetic fields up to 13 T. Applying a magnetic field, a broad anomaly appears below 5 K, which reflects the gap energy between the nonmagnetic ground state singlet and the excited states. The field-dependence of the energy gap estimated from the measured heat capacities gives the critical field values close to those obtained in high-field-magnetization measurements and non-zero gap remaining at the critical field. Within our experimental range of temperature and magnetic field, we have not observed any sharp peaks corresponding to the expected three dimensional magnetic long range ordering.

DOI： 10.1143/JPSJ.61.1772

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Nuclear spin-lattice relaxation times $T_{1}$ of 139La in high-$T_{\text{C } }$ superconductor (La1-xSrx)2CuO4 ($x{=}0.075$, 0.10) have been measured in zero field. $T_{1}^{-1}$ in the superconducting state decreases rapidly, indicating a superconducting energy gap formation, but no signs of $T_{1}^{-1}$ enhancement are observed just below $T_{\text{C } }$. $T_{1}^{-1}$ in the normal state shows slightly stronger temperature dependence than that expected from the Korringa relation ($T_{1}T$${=}$const.) observed in a highly Sr-doped, nonsuperconducting compound with $x{=}0.15$.

DOI： 10.1143/JPSJ.58.2662

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In high-$T_{\text{c } }$ superconductors (La1-xMx)2CuO4 (M$=$Ba, Sr), it has been reported that the heat capacity has a nonzero coefficient $\gamma$ in the temperature linear term. We investigated the detailed dependence of $\gamma$ on Ba doping. It was confirmed that $\gamma$ becomes zero for undoped La2CuO4. With increasing Ba concentration $x$, $\gamma$ increases markedly up to $x{=}0.02$ where the magnetic order almost disappears, while it decreases as superconductivity starts to appear and then has a minimum around $x{=}0.04$. With further increasing $x$, $\gamma$ increases again. These results may be due to a combined effect of two different contributions to $\gamma$.

DOI： 10.1143/JPSJ.57.2261

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DOI： 10.7567/JJAPS.26S3.1253

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DOI： 10.11316/jpsgaiyo.70.1.0_1830

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DOI： 10.11316/jpsgaiyo.69.2.3.0_336_2

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DOI： 10.11316/jpsgaiyo.69.2.3.0_366_1

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

DOI： 10.1143/JPSJ.76.063709

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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Language：Japanese   Publisher：The Physical Society of Japan (JPS)  

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