[en] We grew single crystals of La_2-xSr_xCuO₄ with Sr-concentration gradient along the crystal growth. Doping dependence of the superconducting transition temperature T_c was determined by magnetic susceptibility measurement at different positions of the crystal. The results revealed a dramatic degradation of superconductivity at around x∼0.12 more clearly compared to the previously determined phase diagram using powder samples or single crystals with uniform Sr-concentration

[en] In this paper, we summarize the results of recent neutron scattering and muon spin rotation/relaxation measurements on the magnetic order of the hole-doped La_2-x(Sr,Ba)_xCuO₄ and electron-doped Nd_2-xCe_xCuO₄(NCCO) and Pr_1-xLaCe_xCuO₄(PLCCO). Two types of cuprate exhibit distinct magnetic behaviors upon doping carriers and applying a magnetic field. We also discuss the relation between the magnetic order and superconductivity from a view point of phase separation in both systems

[en] The elastic constant of the vortex lattice is measured in order to estimate the superconducting volume fraction of La_1.875Ba_0.065Sr_0.060CuO₄ which undergoes the structural phase transition to the low-temperature orthorhombic (Pccn) phase. The step like change in the elastic constant of c₄₄ mode of the vortex lattice is clearly observed below T_c, and the saturated value of the elastic constant of the vortex lattice is 68% of the theoretical result for the full-Meissner state. This experimental result indicates that, probing with the vortex lattice, the superconducting volume fraction seems to be about two over three under the so-called stripe order in the Pccn phase

[en] Crystal structure and phonon dynamics up to 150 meV of the spin-Peierls material CuGeO₃ have been investigated by neutron scattering experiments. We found a large lattice anomaly in the a-b plane, vertical to the one-dimensional antiferromagnetic spin chain, associated with additional diffraction peaks in the b^*-axis at temperatures much higher than the spin-Peierls transition temperature. The phonon modes of the chain oxygens at 100 meV show consistent evolution with diffraction. Therefore, we conclude that the structural evolution of the chain oxygens in the a-b plane, which mediates the spin-spin interaction along the c-axis, drives the spin-Peierls transition. (author)

[en] Inelastic neutron scattering data were collected on the high pressure phase of (VO)₂P₂O₇, a S=1/2 Heisenberg antiferromagnetic alternating chain compound. The existence of a spin gap was confirmed, and the size was determined to be Δ=2.15(6) meV (=25.0(7) K). The theoretically predicted second gap (Δ'=2Δ) owing to a 2-magnon bound state was not observed. This is consistent with the high field magnetization measurement reported previously. (author)

[en] We have carried out elastic neutron scattering measurements on La_1.875Ba_0.075Sr_0.05CuO₄ single crystal (T_c≅10 K). Incommensurate elastic magnetic peaks were observed in the low-temperature tetragonal phase with the propagation vector parallel/perpendicular to in-plane Cu-O bond direction. The magnetic peak intensity normalized by the sample volume is approximately six times larger than that of the orthorhombic La_1.88Sr_0.12CuO₄ at low temperature. (author)

[en] Magnetic excitations of La_1.95Sr_0.05CuO₄ were investigated using pulsed neutron inelastic scattering over a wide range of energy up to 300 meV. In contrast to the optimally doped superconductor the dynamical magnetic susceptibility χ^''(ω) around (π,π) in the spin-glass phase monotonically decreases with increasing ω and nearly saturates beyond ∼50 meV. We found that the energy dependence of the q-position in the latter energy region is ascribed to a two-dimensional spin-wave dispersion relation with the nearest neighbor interaction J of 108±6 meV, which is smaller by ∼20% than that of La₂CuO₄

[en] In the last quarter of a century, neutron-scattering measurements have provided important clues for understanding the novel magnetism of carrier doped cuprate oxides. Discovery of evidence for charge-density-wave (CDW) and spin-density-wave (SDW) orders in La_1.6-xNd_0.4Sr_xCuO₄ with x ∼ 1/8 has attracted much attention on the universality of inhomogeneous carrier distribution in CuO₂ planes, namely stripe correlations, and its relevance to the superconductivity. Here we review the nature of charge and spin stripe orders in a prototypical superconducting La-214 system, which has been investigated mainly by neutron scattering measurements. After introducing the hole concentration range, where the each order can be observed, characteristic features of low-energy spin fluctuations in the stripe ordered and disordered La_2-xBa_xCuO₄ with x ∼ 1/8 will be discussed in terms of fluctuating stripes. The impact of magnetic field and impurity substitution on the orders is also presented, followed by a comparative study on electron-doped cuprates. Finally, we will give a brief summary of experimental trends.

[en] A method for calculating the neutron heating rate in plasma systems at densities and temperatures of interest for inertial confinement fusion is presented. The basic equations consist of the transport equations for neutrons and their recoil ions, being written in terms of the modified Eulerian coordinates originally proposed by Wienke (1974). After presenting the calculational model, numerical results are given for a particular test problem, i.e. the deposition of 14-MeV source neutron energy in expanding D-T spheres. It is shown that the energy transport by recoil ions has a considerable influence on the neutron heating. Calculations neglecting recoil-ion transport fail to account for the temperature dependence of neutron heating and over-estimate the deposition to plasma ions. (author)

[en] We performed systematic post-growth heat treatments on sizable single crystals of Nd_1.85Ce_0.15CuO₄. The superconducting transition temperature, T_c, and its distribution in the sample are both sensitive to details of the heat treatment and sample size. With refinement of the heat treatment conditions we have succeeded in preparing two distinct superconducting samples in which T_c equals 18K and 25K under identical Ce-concentrations. Neutron scattering experiments initially observed nonmagnetic super-structure peaks at (π, π) only in the reduced superconducting phase. Atomic displacement in this structure is different from that induced by in-plane rotation of CuO₄ squares as previously reported for Gd_2-xCe_xCuO₄. A possible relationship between atomic displacements and superconductivity and the role of reduced heat treatments are discussed from the viewpoint of carrier localization. (author)