Teruhiko Akazawa

Pressure-induced superconductivity in UIr

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 ...

Pressure-Induced Superconductivity Emerging from Antiferromagnetic Phase in CeNiGe3

The antiferromagnet CeNiGe 3 exhibits superconductivity under pressure. The Neel temperature initially increases with increasing pressure up to 3 GPa and then becomes zero at a critical pressure ( ...

Pressure-Temperature Phase Diagram and Superconductivity in UIr

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.

Anomalous Magnetic Transition in UNiSn.

In concurrence with an antiferromagnetic transition at T N ≃43 K, UNiSn undergoes a semiconductor-to-metal phase transition. The powder X-ray diffraction reveals that the complex transition is accompanied also by a structural transition from a cubic to tetragonal symmetry. The temperature dependence of lattice parameters and that of Mossbauer spectra suggest that the transition is of first order and is a cooperative phenomenon of the structural and magnetic instabilities. However, an elastic modulus behaves as if the transition were of second order. This puzzle is solved by a scenario based on the crystalline-electric-field for 5 f 2 configuration in U 4+ with the ground state of a non-magnetic doublet Γ 3 in the cubic phase.

Fundamental studies of helical-type seawater MHD generation system

A new MHD (magnetohydrodynamics) generator based on electromotive force using seawater, that is, a helical-type seawater MHD generator with a 7 T solenoid superconducting magnet, is designed, constructed and tested. The constructed generator contains a helical insulation wall made of polyvinyl chloride 140 mm long and 100 mm in diameter, an anode rod made of SUS316 1350 mm long and 10 mm in diameter, and a cathode pipe made of SUS316 260 mm long and 100 mm in diameter. In the experiment, electromotive force and generator output are measured in terms of average flow velocity (0-5.6 m/s) and magnetic field (0-7 T) using artificial seawater (3.4% NaCl aqueous solution). As a result of the experiment, it was found that the electromotive force increases proportionally to average flow velocity and magnetic field, and that the generator output increases quadratically to average flow velocity and magnetic field over certain points. Experimental values are discussed by comparing the theoretical values and computed values.

Quadrupolar and Magnetic Phase Diagram of UNiSn

UNiSn undergoes a multiplex transition from a paramagnetic semiconductor (Phase I) to an antiferromagnetic metal with ferroquadrupolar order (Phase III) at T N ∼43 K in zero field. We have measured elastic moduli, thermal expansion, magnetization and electrical resistivity of UNiSn in magnetic field. Magnetic field raises the quadrupole-ordering temperature T Q , which was found to be identical to the semiconductor-metal transition temperature T SM , while T N is nearly field-independent. We observed a separation of T N and T Q in high magnetic field above ∼4 T, and we found a new phase (Phase II) between T N and T Q , which has been identified as a paramagnetic metal with ferroquadrupolar order. The coincidence of T Q and T SM strongly suggests that the ferroquadrupolar order is responsible for a change in electronic structure, leading to metallic conduction.

Flow control of seawater with a diverging duct by MHD separation method

A unique control method for a diverging seawater flow based on electromagnetic force, the so-called MHD (magnetohydrodynamics) separation method, is performed. The experimental apparatus is composed of a 10-T class superconducting magnet, a separation cell, a seawater tank, and a flow system. The constructed separation cell contains parallel electrodes, 18 mm wide, 40 mm long and 20 mm apart, and a diverging duct divided into equal parts, A (not affected by electromagnetic force) and B (affected by electromagnetic force). The dependence of flow ratio (mass of side-A sample solution/total mass of sample solution) on electric current, magnetic field, NaCl concentration and sample velocity has been studied experimentally using NaCl aqueous solution. The possibility of flow control of seawater with a diverging duct by the MHD separation method as well as experimental results are discussed.

NMR and Specific Heat of YCo12B6 and LaCo12B6

NMR measurements were made for YCo 12 B 6 and LaCo 12 B 6 mainly by the steady-state method in zero external field as a function of temperature. Two 59 Co domain signals with quadrupole splittings and two wall signals with single lines were observed. With decreasing temperature, a low-frequency domain signal in LaCo 12 B 6 vanished below about 25 K but another domain signal emerged below about 40 K, revealing a discontinuous change in frequency and in spacing between the quadrupole-split components. The specific heat of LaCo 12 B 6 did not show any anomaly in this temperature range. These suggest that the observed change in NMR in LaCo 12 B 6 around 35 K is not of first order but is presumably associated with a change in magnetic states. In YCo 12 B 6 there was no such a discontinuous change in the NMR spectrum.

Multi-push Display using 6-axis Motion Platform

This study designed and developed a novel tactile display that provides a multi-push sensation by using a 6-axis motion platform. The display mechanically controls the position and orientation of a surface panel. A user touching an on-screen button with one finger can push the button vertically. When the user subsequently touches the display with a second finger, the surface panel declines and the position of the first finger remains unchanged. Thus, the user can push at two positions on the surface panel. We also developed a prototype system with six servomotors and a touch panel based on the principle of frustrated total internal reflection.

Pressure-temperature phase diagrams of some heavy fermion systems

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.