We present the experimental results of DC magnetization measurements on the bilayer manganese oxide (Pr 0.6 La 0.4 ) 1.2 Sr 1.8 Mn 2 O 7 under pressure. The data were taken to elucidate the magnetic properties of the field-induced ferromagnetic phase and to establish the magnetic phase diagram on the fields applied along the c -axis. The results indicated that the phase is sensitive to the applied pressure. The isothermal remanent magnetization M IRM ( t ) as a function of time t in the ferromagnetic phase suggests the existence of the relaxation process and its pressure effect. It seems that the effect of pressure leads to a variation of the transition probability between the ferromagnetic metal and paramagnetic insulating state.

We have measured the thermal expansion coefficient αL(T) of SmS under pressure up to 21.6kbar. In the golden phase, an excitation gap Δ inferred from αL(T) decreases with increasing pressure. When the system enters the metallic phase from the golden phase, Δ collapses suddenly to zero, and simultaneously, a huge sharp anomaly appears in the αL(T) curve, reflecting the magnetic phase transition.

We investigated the effect of pressure on the magnetic properties of a single crystal of the bilayer manganese oxide (Pr0.6La0.4)1.2Sr1.8Mn2O7 by means of DC magnetization measurements under pressure. The ferromagnetic transition, which is accompanied by a metal–insulator transition, is highly sensitive to pressure. The pressure causes a structural variation, which affects the magnetic properties. We discuss the pressure dependence of the 3d electronic state of the Mn ion in this system.

YbInCu4 undergoes a first‐order isostructural valence transition at TV = 42 K, which is accompanied by a 0.5% volume increase due to cooling. In order to elucidate the valence transition, both the linear thermal expansion and magnetostriction, ΔL/L, of a YbInCu4 single crystal were measured using strain gauges under high pressures of up to 3.0 GPa and a magnetic field of up to 18 T. The abrupt volume change during the valence transition was confirmed to decrease linearly with TV under a high pressure. It was also observed that TV was suppressed upon application of a magnetic field. On the basis of the results, we have established a T‐P‐B phase diagram for the first‐order valence transition in YbInCu4.

We report electrical resistivity on a single crystal of the hole-doped two-leg ladder compound Sr2Ca12Cu24O41, which becomes superconducting with T(c)similar to 5 K only at pressures above similar to 3.0 GPa. Measurements were performed at nearly hydrostatic pressures up to 5.7 GPa and low temperatures down to 100 mK under static magnetic fields up to 20 T parallel to the a axis (along the ladder rungs) and up to 7 T parallel to both the b axis (perpendicular to the ladder plane) and the c axis (along the ladder legs). A clear difference in the resistive upper critical field H-c2(T) is observed among these three directions, confirming that this system has a highly anisotropic superconducting ground state. Also, H-c2(T) parallel to the ladder plane is found to exceed the Pauli limit by a factor of more than 2, suggesting either a strong spin-orbit scattering or spin-triplet pairing. Furthermore, it is implied, from measurements of resistivity versus angle of magnetic field in the bc plane, that another superconducting phase is stable below around 3 K only when the magnetic field is applied exactly along a certain direction that is +/- 35 degrees from the ladder direction.

A series of molecular conductors β ′-( cation )[Pd(dmit) 2 ] 2 ( cation = Et 2 Me 2 P and Me 4 P) exhibit various complicated pressure-induced phenomena. Resistivity measurements under high pressure up to 8 GPa have been carried out using a clamp-type piston-cylinder cell and cubic anvil type high pressure apparatus. The Et 2 Me 2 P salt shows non-metallic phases at low and high pressure regions, between which a metallic phase appears. The application of pressure suppresses the low-temperature resistivity of this salt. However, the non-metallic behavior still remains at low temperature under 8 GPa. For the Me 4 P salt, the metal-to-non-metal transition temperature reaches a minimum at 0.83 GPa and turns to increase with increasing pressure up to 8 GPa, showing no metallic state stable at low temperature

Electrical resistivity measurements of the insulating Ba1−xKxBiO3 (x = 0, 0.15) under high pressure up to 8 GPa have been performed in order to search for the pressure-induced superconductivity, using a cubic-anvil pressure system. A polycrystal of BaBiO3 has been prepared by the solid-state reaction method. A single crystal of Ba0.85K0.15BiO3 has been synthesized by the electrochemical method from molten salts. The electrical resistivity of both compounds slightly decreases with increasing pressure. However, the temperature dependence still remains semiconductive and no superconductivity is observed.

We report the highest transition temperature of quadrupolar ordering [T-Q] in YbAl3C3, where a distinct anomaly is observed by specific heat and ultrasonic measurements at 80 K. Magnetization measurements show only a very slight change and no magnetic or structural phase transitions can be observed by neutron diffraction measurements in this temperature range. Therefore, we believe that YbAl3C3 Shows an antiferroquadrupolar ordering with the highest T-Q found to date and is the first realization of this ordering beyond liquid nitrogen temperatures for rare-earth and actinide intermetallic compounds.

SmS exhibits a pressure-induced phase transition at 0.6GPa from a semiconducting state to a rather metallic state accompanied with a change of Sm valence and volume compression. Using the X-ray diffraction technique under high pressures, we found local minima of the lattice constant of SmS in the metallic phase up to near 2GPa. The pressure region of the volume minima coincides with that of the low-temperature increase and the humps of electrical resistivity. We succeeded in reproducing the volume minima by a phenomenological model of a Schottky-type behavior due to electronic gap suppressed by pressure.

Pressure-induced superconductivity in a spin-ladder cuprate Sr2Ca12Cu24O41 was investigated on the microscopic level by using 63Cu nuclear magnetic resonance (NMR) under pressure of 3.5GPa. We observed both spin and superconducting gaps in separated temperature regions. We found that the superconducting state possesses a full gap and is quite stable even at high fields close to the conventional Pauli limit.

This paper reports the measurements of resistance (R) and magnetoresistance of NbSe3 near the critical pressure (P-c = 7.5 kbar), where the lower charge-density-wave (CDW) phase is on the verge of destruction. For P = 7.6 kbar, the temperature dependence of dR/dT exhibits a weak anomaly at T* 15 K and the superconducting transition is observed at T-c = 2.8 K. From the observation of a large magnetoresistance due to an imperfect nesting of Fermi surface, we show that the weak anomaly is closely related to the lower CDW phase. Moreover, an excess conductance and violation of Kohler's rule are found below similar to T*. The origins of the excess conductance and the violation of Kohler's rule are discussed in terms of charge fluctuation associated with the lower CDW state.

The electrical resistivity rho(T) of Y1-xUxPd3 (x = 0, 0.05 and 0.2) and the lattice constants for x = 0 have been measured at high pressure. It is found that the cubic Cu3Au structure is stable up to 12 GPa at room temperature. The Kondo temperature T-K was extracted from the rho(T) curve and it was found that it increases with pressure. A logarithmic temperature dependence characteristic of the Kondo effect was found for x = 0.2 in the temperature range above about 0.5 T-K. Fermi liquid behaviour in rho(T) for x = 0.05, i.e., rho(T) proportional to T-2, is observed and its stability at high pressure is discussed. The pressure dependence of the Kondo temperature T-K is discussed using the Gruneisen parameters at T-K, Gamma(K). It appears that the values Of Gamma(K) are the same for these two compounds (x = 0.05 and 0.2): Gamma(K) = 12. The T-linear behaviour in p(T) for x = 0.2, which is characteristic behaviour for non-Fermi liquids, is collapsed by an application of pressure and typical Fermi liquid quadratic temperature dependence recovers at high pressure. From the result for x = 0.2, the power n of the temperature in rho(T) proportional to T-n is determined as 1.0 at ambient pressure and 1.9 at 5.8 GPa. It is pointed out that the hybridization effect due to the application of pressure gives rise to a crossover from a non-Fermi liquid state to Fermi liquid state. But the crossover temperature T-cr shows a pressure dependence different from that predicted by the two-channel Kondo model.

Physical properties of an organic conductor, β'-(BEDT-TTF) 2 IBrCl, were characterized under ambient and extremely high pressures. Semiconducting behavior with activation energy, E a =0.11eV, and antiferromagnetic transition with T N =19.5K were uncovered in the present work. In addition, we have found that this salt showed a sign of superconductivity at 8.0GPa in common with the case of the β'-(BEDT-TTF) 2 ICl 2 , which is the highest-T c superconductor among organics.

An atomic-scale graded structure has been formed previously in a Bi70Sb30 (at. %) alloy that is miscible in all proportions, by sedimentation of substitutional solute atoms under an ultrastrong gravitational field up to 1×106 G at 220–240 °C [T. Mashimo, T. Ikeda, and I. Minato, J. Appl. Phys. 90, 741 (2001)]. In this study, additional megagravity field experiments were performed on the Bi70Sb30 alloy and pure Bi at different temperatures below their melting points, to investigate the change in crystalline state under the ultrastrong gravitational field. For the Bi70Sb30 alloy ultracentrifuged at 191–205 °C, no change in composition was observed, and the grain sizes of the crystals decreased from several millimeters to tens of micrometers, while no distinct change in grain size was observed for the pure Bi ultracentrifuged under the same experimental conditions. The Bi70Sb30 alloy ultracentrifuged at 220–240 °C consisted of two regions with different morphologies–fine-grained crystals with grain sizes in the range of tens of micrometers in the low gravity region, and large crystals with grain sizes several millimeters long and hundreds of micrometers wide along the direction of gravity in the high gravity region, where sedimentation of atoms was confirmed. The large crystals with hexagonal structures were formed by preferential crystal growth roughly along the c axes, and a large strain that increased as the gravitational field increased existed inside these crystals. Formation of this anomalous crystal state might be correlated with the sedimentation of atoms.

We have succeeded in growing single crystals of Ca3Ru2O7 using a floating-zone method. The temperature dependence of the electrical resistivity establishes that Ca3Ru2O7 develops a quasi-two-dimensional metallic ground state below 30 K, from which the observed quantum oscillation derives. The temperature dependence of specific heat reveals the electronic specific-heat coefficient gamma to be as small as 1.7 mJ/Ru mol K-2. A qualitative difference exists between the field dependences of rho(ab) and rho(c). The field dependence of the resistivity at the metamagnetic transition around 6 T can be explained from the tunneling magnetoresistance.

The dc electrical resistivity ρ in the reduced hexagonal BaTiO 2.98 single crystal was measured under hydrostatic pressures up to 3.1 GPa in the temperature range of 5 K to 300 K. The ρ along the hexagonal c axis is somewhat larger than that of the perpendicular direction. The ρ vs T curve changes the behavior at the temperature T 0 , where the hexagonal to orthorhombic phase transition takes place: it behaves as a semiconductor and a metal at temperatures below and above T 0 , respectively. With increasing pressure T 0 decreases, and the metallic behavior dominates whole of the temperature range at pressures above p c =1.9 GPa. In the pressure-induced metallic phase, T 2 -dependence of resistivity appears at low temperatures. This rule suggests that electrons in the Ti 3 d band of BaTiO 3 are the same as electrons in a strongly correlated electron system. A band model is proposed to explain such insulator–metal transitions in SrTiO 3 , cubic BaTiO 3 , and hexagonal BaTiO 3 .

An ultracentrifuge apparatus, which can generate an ultra-strong gravitational field even >1 000 000 (1 million) G (1 G=9.8 m/s2) over a wide temperature range up to >500 °C with high stability control, was developed for new materials science research. The system consists of an air turbine motor with ceramic ball bearings and dumper section, a sample rotor with an outer diameter of up to 160 mm, a vacuum chamber, and a heating system. The nonbored rotor and the double-structural dumper bushing are used to raise the maximum rotational speed and to improve the stability. The samples can be heated by radiant heat. A maximum rotational speed of 190 000 rpm using a 70 mm diam rotor was recorded despite a short time where the maximum gravitational field was >1 2000 000 G. Long and high-temperature ultracentrifuge experiments using 70 and 80 mm diam rotors made of titanium alloy with rotational speeds of up to 170 000 rpm even at temperatures of over 200 °C for 100 h with ripples of <0.05% and <1°, respectively, were successfully performed, where the maximum gravitational field of the sample was >1 000 000 G. The potential energy and sample volume were increased by factors of >2 and >4, respectively, compared with those in the Kumamoto University study [T. Mashimo, S. Okazaki, and S. Tashiro, Rev. Sci. Instrum. 67, 3170 (1996)].

CeRh2Si2 shows two successive antiferromagnetic phase transitions at ambient pressure (TN1=36K and TN2=27K). Application of pressure suppresses TN1 to 0K at Pc∼1GPa. We study the magnetism of the single-crystalline sample of CeRh2Si2 by muon spin rotation/relaxation (μSR) method up to 0.45GPa. Below TN2, we observed both the spontaneous muon spin precession and the fast muon spin relaxation under zero magnetic field. Although the transition temperature decreases with increasing the pressure, the precession frequency, which is proportional to the saturated sublattice magnetic moment, is nearly independent of the pressure.