Giant Magnetoresistance Effect in the Metal-Insulator Transition of Pyrochlore Oxide Nd2Ir2O7

We investigated the magnetoresistance (MR) effect of the pyrochlore oxide Nd2Ir2O7, which shows a metal-insulator transition at T_MI =33 K. A small positive MR effect was observed in the metallic state above T_MI, while a large negative MR effect was observed in the insulating state below T_MI . MR effects exceeding 3000% were found at 1 K at a field of 9 T. As a result, we confirmed the crossover from the insulating state to a state with a small or partial band gap in a field up to 56 T. Furthermore, from the MR effect in Eu2Ir2O7 (T_MI = 120 K) and Gd$_2$Ir$_2$O$_7$ (T_MI = 127 K), we revealed that the large negative MR effect of the pyrochlore iridate Ln2Ir2O7 depends on the magnetism of the lanthanide Ln^{3+} ion. The d-f interaction plays a significant role in the large negative MR effect in the insulating state.Comment: 10 pages, 4 figure

Numerical simulation of liquid sloshing in a partially filled container with inclusion of compressibility effects

A numerical scheme of study is developed to model compressible two-fluid flows simulating liquid sloshing in a partially filled tank. For a two-fluid system separated by an interface as in the case of sloshing, not only a Mach-uniform scheme is required, but also an effective way to eliminate unphysical numerical oscillations near the interface. By introducing a preconditioner, the governing equations expressed in terms of primitive variables are solved for both fluids (i.e. water, air, gas etc.) in a unified manner. In order to keep the interface sharp and to eliminate unphysical numerical oscillations in unsteady fluid flows, the non-conservative implicit Split Coefficient Matrix Method (SCMM) is modified to construct a flux difference splitting scheme in the dual time formulation. The proposed numerical model is evaluated by comparisons between numerical results and measured data for sloshing in an 80% filled rectangular tank excited at resonance frequency. Through similar comparisons, the investigation is further extended by examining sloshing flows excited by forced sway motions in two different rectangular tanks with 20% and 83% filling ratios. These examples demonstrate that the proposed method is suitable to capture induced free surface waves and to evaluate sloshing pressure loads acting on the tank walls and ceiling

Magnetic order in pyrochlore iridate Nd2_2Ir2_2O7_7 probed by muon spin relaxation

Muon-spin relaxation results on the pyrochlore iridate Nd$_2$Ir$_2$O$_7$ are reported. Spontaneous coherent muon-spin precession below the metal-insulator transition (MIT) temperature of about 33 K is observed, indicating the appearance of a long-ranged magnetic ordering of Ir$^{4+}$ moments. With further decrease in temperature, the internal field at the muon site increases again below about 9 K. The second increase of internal field suggests the ordering of Nd$^{3+}$ moments, which is consistent with a previous neutron experiment. Our results suggest that the MIT and magnetic ordering of Ir$^{4+}$ moments have a close relationship and that the large spin-orbit coupling of Ir 5\textit{d} electrons plays a key role for both MIT and the mechanism of the magnetic ordering in pyrochlore iridates in the insulting ground state.Comment: 5 pages, 3 figures. Accepted by Physical Review B (rapid communications

Transport properties in normal metal Bi2Pd3S2 and superconducting Bi2Pd3Se2

The transport properties of the parkerite-related compounds Bi2Pd3X2 (X=S,Se) were studied. The electrical resistivities of both compounds show typical metallic behavior up to 400 K. Resistivity and specific heat measurements at low temperatures reveal that Bi2Pd3Se2 is superconducting below 1 K. On the other hand, Bi2Pd3S2 does not show a bulk superconducting transition down to 0.35 K. In the normal state, the electronic specific heat coefficient γ and the Debye temperature θD are found to be 5.9 mJ/mol K2 and 170 K, respectively for Bi2Pd3S2, and 8.3 mJ/mol K2 and 150 K, respectively for Bi2Pd3Se2. In the superconducting state for Bi2Pd3Se2, the upper critical field at zero temperature for Bi2Pd3Se2 is 290 mT. From the electronic specific heat in the superconducting temperature range, it was found that Bi2Pd3Se2 belongs to an s-wave weakcoupling superconductor

Metal–Insulator Transitions in Pyrochlore Oxides Ln2Ir2O7

We report the physical properties of Ln2Ir2O7 (Ln = Nd, Sm, Eu, Gd, Tb, Dy, and Ho), which exhibit metal-insulator transitions (MITs) at different temperatures. The transition temperature TMI increases with a reduction in the ionic radius of Ln. The ionic radius　boundary for MITs in Ln2Ir2O7 lies between Ln = Pr and Nd. MITs in Ln2Ir2O7 have some common features. They are second-order transitions. Under the field cool condition, a weak ferromagnetic component (»10−3 μB/f.u.) caused by Ir 5d electrons is observed below TMI.The entropy associated with MITs for Ln = Nd, Sm, and Eu is estimated to be 0.47, 2.0, and 1.4 J/K mole, respectively. The change in entropy is much smaller than 2R ln 2 [11.5 J /K mole] expected in a magnetic transition due to localized moments of S = 1/2. The feature of continuous MITs in Ln2Ir2O7 is discussed

Neutron scattering study of dipolar spin ice Ho2Sn2O7: Frustrated pyrochlore magnet

By means of neutron scattering techniques we have investigated the frustrated pyrochlore magnetHo2Sn2O7, which was found to show ferromagnetic spin-ice behavior below T.1.4 K by susceptibilitymeasurements. High-resolution powder neutron diffraction shows no detectable disorder of the lattice, whichimplies the appearance of a random magnetic state solely by frustrated geometry, i.e., the corner sharingtetrahedra. Magnetic inelastic scattering spectra show that Ho magnetic moments behave as an Ising spinsystem at low temperatures and that the spin fluctuation has static character. The system remains in a shortrange-ordered state down to at least T50.4 K. By analyzing the wave-vector dependence of the magneticscattering using a mean-field theory, it is shown that the Ising spins interact via the dipolar interaction.Therefore we conclude that Ho2Sn2O7 belongs to the dipolar-spin-ice family. Slow spin dynamics is exhibitedas thermal hysteresis and time dependence of the magnetic scattering

Charge-density-wave superconductor Bi2Rh3Se2

We discovered a superconducting transition with the charge-density-wave state in a ternary compound Bi2Rh3Se2. This compound crystallizes in the parkerite-type structure composed of sheets containing one-dimensional Rh-Rh chains. The electrical resistivity, magnetic susceptibility, thermoelectric power, sample length change, and x-ray diffraction measurements reveal that this compound is in the CDW state below 240 K. Furthermore, the specific heat and electrical resistivity measurements show a superconducting transition at ~0.7 K. The various superconducting parameters were determined, and the GL parameter (0) shows the considerably large value of 151 indicating an extreme type-II superconductor

Metal–Insulator Transitions in Pyrochlore Oxides Ln2Ir2O7

We report the physical properties of Ln2Ir2O7 (Ln = Nd, Sm, Eu, Gd, Tb, Dy, and Ho), which exhibit metal-insulator transitions (MITs) at different temperatures. The transition temperature TMI increases with a reduction in the ionic radius of Ln. The ionic radius　boundary for MITs in Ln2Ir2O7 lies between Ln = Pr and Nd. MITs in Ln2Ir2O7 have some common features. They are second-order transitions. Under the field cool condition, a weak ferromagnetic component (»10−3 μB/f.u.) caused by Ir 5d electrons is observed below TMI. The entropy associated with MITs for Ln = Nd, Sm, and Eu is estimated to be 0.47, 2.0, and 1.4 J/K mole, respectively. The change in entropy is much smaller than 2R ln 2 [11.5 J /K mole] expected in a magnetic transition due to localized moments of S = 1/2. The feature of continuous MITs in Ln2Ir2O7 is discussed

The Specialist Committee on Wake Fields Final Reports and Recommendations to the 25th ITTC

The recommended actions of 25th ITTC Specialist Committee on Wake-Fields, as stated above are focused on two main areas, the review of the numerical prediction and experimental measurement (methods) of wakefields and the review and development of ITTC procedures

関西系製糸企業の戦後戦略展開を比較分析することから導かれる成熟産業の脱成熟化戦略とそのための経営資源に関する研究

甲南大学平成10年度(1998年度