Nobuo Mori

Advanced high-temperature ultracentrifuge apparatus for mega-gravity materials science

An ultracentrifuge apparatus, which can generate an ultra-strong gravitational field even >1u200a000u200a000 (1 million) G (1 G=9.8 m/s2) over a wide temperature range up to >500u200a°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 190u200a000 rpm using a 70 mm diam rotor was recorded despite a short time where the maximum gravitational field was >1u200a2000u200a000 G. Long and high-temperature ultracentrifuge experiments using 70 and 80 mm diam rotors made of titanium alloy with rotational speeds of up to 170u200a000 rpm even at temperatures of over 200u200a°C for 100 h with ripples of <0.05% and <1°, respectively,...

Material properties of Ni–Cr–Al alloy and design of a 4 GPa class non-magnetic high-pressure cell

The Ni–Cr–Al Russian alloy was prepared. Its magnetic and mechanical properties were better than those of MP35N alloy. We fabricated the a piston–cylinder-type hybrid high-pressure cell using the Ni–Cr–Al alloy. It has been found that the maximum working pressure can be repeatedly raised to 3.5 GPa at T = 2 K without any difficulties.

Effects of ultrastrong gravitational field on the crystalline state of a Bi-Sb alloy

An atomic-scale graded structure has been formed previously in a Bi70Sb30 (at.u200a%) alloy that is miscible in all proportions, by sedimentation of substitutional solute atoms under an ultrastrong gravitational field up to 1×106u200aG at 220–240u200a°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 191–205u200a°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 220–240u200a°C consisted of two regions with different morphologies–fine-grained crystals with grain sizes in ...

Effect of pressure on the electrical resistivity of a single crystal of YbInCu4

Abstract Temperature-dependent electrical resistivity measurements have been performed on single-crystalline YbInCu4 under hydrostatic pressures to P=3.3xa0GPa. Its valence phase-transition temperature TV decreases linearly at a rate of −2.0xa0K/GPa with increasing pressure to 1.0xa0GPa, as found previously. Above 1.0xa0GPA, however, TV decreases more gradually and is depressed to below 1.5xa0K at 2.5xa0GPa. Experimental results suggest that the hybridization between 4f- and conduction-band electrons is reduced with increasing pressure and that the semi-metallic state (T>TV) is favored over the metallic state (T

High-Pressure Study up to 9.9 GPa of Organic Mott Insulator, β'-(BEDT-TTF)2AuCl2

We have investigated the resistivity of an organic Mott insulator, β-(BEDT-TTF) 2 AuCl 2 , under extremely high pressures of up to 9.9 GPa, using the cubic anvil press, motivated by the fact that ...

Uniaxial Strain Effect on TV and Electrical Resistivity in Magnetite (Fe3O4)

Magnetization and electrical resistivity studies are reported for a single crystal of magnetite under uniaxial strain applied along the [110] and [100] directions. The metal‐insulator transition temperature, TV, shifted to higher temperatures with increasing uniaxial compression which is opposite to the result obtained under hydrostatic pressure. Furthermore, the electrical resistivity was found to increase at temperatures below TV, and to decrease at temperatures above TV, with increasing uniaxial compression. Differences between the present results and those under hydrostatic pressure are discussed.

Nuclear magnetic relaxation under high pressure in the spin ladder Sr2Ca12Cu24O41

Abstract Nuclear magnetic resonance (NMR) under pressure below 3xa0GPa was performed by using a single crystal of Sr 2 Ca 12 Cu 24 O 41 to investigate the spin dynamics on the critical regime neighboring the superconducting phase. The temperature dependence of the relaxation rate 1/ T 1 deviates from an activated type below 50xa0K and exhibits power law behavior. On the other hand, 1/ T 1 increases as pressure is increased at low temperatures. These features are intrinsic to this system and reflect some fluctuations originating from holes.

High pressure studies of anomalous electronic states of Y1?xUxPd3

The electrical resistivity ρ(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 TK was extracted from the ρ(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 0.5TK. Fermi liquid behaviour in ρ(T) for x = 0.05, i.e., , is observed and its stability at high pressure is discussed. The pressure dependence of the Kondo temperature TK is discussed using the Gruneisen parameters at TK, ΓK. It appears that the values of ΓK are the same for these two compounds (x = 0.05 and 0.2): ΓK = 12. The T-linear behaviour in ρ(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 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 Tcr shows a pressure dependence different from that predicted by the two-channel Kondo model.

μSR study of magnetism of CeRh2Si2 under a high pressure

Abstract CeRh2Si2 shows two successive antiferromagnetic phase transitions at ambient pressure (T N 1 =36 K and T N 2 =27 K ). Application of pressure suppresses TN1 to 0 K at P c ∼1 GPa . We study the magnetism of the single-crystalline sample of CeRh2Si2 by muon spin rotation/relaxation (μSR) method up to 0.45 GPa . 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.

Observation of crystalline state of the graded structure BiSb alloy prepared under a strong gravitational field of around 1 million G

An atomic-scale graded structure had been formed in an all-proportion miscible alloy in bismuth (Bi)-antimony (Sb) (70:30 in mol%) system by the sedimentation of substitutional solute atoms under a strong gravitational field of 1 million G level in maximum acceleration at 220–240□ (Mashimo et al. 1997, Mashimo et al. 2001). The large and long crystals whose grain sizes were several mm long and several hundreds of μm wide were oriented along the direction of gravity in the high gravity region larger than about 0.7×106 G, while those of the small crystals in the low gravity region smaller than it were several 10 Pin. It was found that the large strain existed in the large crystals by back-reflection Laue method. It was found that the c axis of hexagonal structure of a large crystal was roughly parallel to the direction of gravity by Transmission Electron Microscopy (TEM) observation.