Y. Hidaka

Determination of Space Group and Refinement of Structure Parameters for La2CuO4-δ Crystals

The space group in the orthorhombic phase of La2CuO4-δ was confirmed to be Cmca for both as grown and deoxygenated crystals by using conventional and convergent beam electron diffraction together with high resolution neutron powder diffraction methods. The Rietveld refinements of neutron powder diffraction data determined the structural parameters. Slight differences in lattice constants, positional parameters and occupation factor for oxygen atoms were found between the two crystals.

Antiferromagnetic ordering of Cu ions in NdBa2Cu

Neutron-scattering experiments performed on single crystals NdBa/sub 2/Cu/sub 3/O/sub 6.1/ reveal antiferromagnetic order for T

Neutron powder diffraction from polymorphs of BaPb0.75Bi0.25O3

Crystal structures of three polymorphs of the superconducting oxide BaPb0.75Bi0.25O3 have been determined by high-resolution neutron powder diffraction. The compound has been confirmed to form both tetragonal (I4/mcm) and orthorhombic (Ibmm) structures at room temperature. The latter transforms to the monoclinic phase (P21/m) at low temperatures. The structural difference of the three polymorphs has been described by the rotation as well as the distortion of oxygen octahedra surrounding the Pb0.75Bi0.25 cations.

Dynamic Spin Properties of La1.98Sr0.02CuO4

Neutron scattering experiments have been performed to study the dynamic spin properties of La 1.98 Sr 0.02 CuO 4 , a crystal with just enough Sr to destroy three-dimensional long range magnetic order and induce spin-glass behavior at low temperatures. The q -integrated susceptibility \(\int \,{\rm d}^{2}q_{\rm 2D}\,{\rm Im}\,\chi _{\rm 2D}(q_{\rm 2D},\,\omega )\) follows the scaling function of ω/ T suggested by Keimer et al. Below 3 meV, however, clear deviation from the scaling function is observed at low temperatures. This probably originates from a gap in the spin-wave-like excitations due to the out-of-plane anisotropy.

Space-Group Determination of La2CuO4-δ by Conventional and Convergent-Beam Electron Diffraction

The space group of La2CuO4-δ (δ≤0.02-0.03) was unambiguously determined to be Pccn by conventional and convergent-beam electron diffraction. It was found that all of as-grown, oxidized and deoxidized crystals belong to the same space group. The atomic positions do not appear to differ greatly from those given for (La1-xBax)2CuO4-δ by Onoda et al. (Jpn. J. Appl. Phys. Lett. 26 (1987) L363).

Phonon density of states of super and non-superconducting states in La1.85Sr0.15Cu1−xZnxO4(x=0, 0.02)

Abstract We have observed a sharpening in the phonon density of states (PDOS) on the Cu-O(1) bond stretching mode in the CuO 2 plane for superconducting La 1.85 Sr 0.15 CuO 4 , while Zn doping has the same effect on the PDOS as rising temperature on the superconducting sample.

Antiferromagnetism in NdBa2Cu3O6.1

Abstract Neutron scattering experiments performed on single crystals of NdBa 2 Cu 3 O 6.1 reveal antiferromagnetic order for T T N = (385 ± 2) K in which the structure is characterized by the magnetic wave vector ( 1 2 , 1 2 , 1 2 ) . The magnetic intensities are accounted for by Cu 2+ spins coupled antiferromagnetically in the CuO 2 planes. The oxygen-deficient layers exhibit a small staggered magnetization ϵ S which induces the spin ordering - S , -ϵ S , - S , + S , +ϵ S , + S , along the tetragonal axis. The average staggered magnetization evaluated at room temperature is about 0.40μ B in the CuO 2 planes and about 0.04μ B in the oxygen-deficient layers.

SPINS AND CARRIERS IN OXIDE SUPERCONDUCTORS STUDIED BY RAMAN SCATTERING

The spin and doped charge states in copper oxide superconductors were investigated by Raman spectroscopy. The anomalous magnon scattering in the antiferromagnetic insulator phases, such as the second peaks near 4J (J is the two-spin superexchange energy) in the B1g spectra and the large scattering intensities in the A1g spectra, suggests the existence of four-spin cyclic exchange interactions. When carriers are doped, the A1g spectra show non-“normal Fermi liquid” behavior. The imaginary part of the experimentally obtained susceptibility have ω-proportional part from ω~0. The gradient increases, on cooling, as in the case of the marginal Fermi liquid.

Magnetic phase transitions and spin correlations in cupreous superconductors and their progenitors

A novel class of superconducting oxides commonly form the CuO 2 lamellars. Neutron scattering experiments revealed the existence of the antiferromagnetic long range order in the undoped progenitors. The local crystal symmetry around Cu 2+ governs the antiferromagnetic structure and related magnetic phase transitions. The two dimensional antiferromagnetic spin correlations persisting even in the superconducting states is discussed in our view that the magnetism has-an intimate relation to the appearance of the high temperature superconductivity.

Two Dimensional Quantum Spin Fluid — Progenitor of High Temperature Superconductivity —

Neutron scattering probed novel two dimensional antiferromagnetic spin correlations in pure La2CuO4 which is the mother compound of high temperature superconductors of doped La2-xMxCuO4. Cu2+ moments are ordered instantaneously over very large areas in the CuO2 plane but there is no measurable time averaged staggered moment. Since the dynamical behavior observed is much akin to that in the quantum antigerromagnetic chain, we concluded that spin fluctuations observed at finite temperatures are quantum spin liquid state like that in quantum antiferromagnetic chain at T = 0.