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The effect of competing crystal-field anisotropies on magnetic order has been investigated in a series of Ho/Er superlattices using neutron and resonant X-ray magnetic diffraction techniques. The neutron diffraction reveals that for temperatures in the interval T-N(Er) less than or equal to T less than or equal to T-N(Ho) the Ho basal-plane order propagates coherently through the paramagnetic Er, and that below T-N(Er) the longitudinal component of the Er moments fail to order across the Ho block. The magnetic superlattice peaks observed in the X-ray scattering display an anomalous energy dependence: a sharp resonance is found at L(III)(Ho), with no resonance visible at L(III)(Er). These results are discussed with reference to models of exchange in metallic superlattices.

The effect of competing crystal-field anisotropies on magnetic order has been investigated in a series of Ho/Er superlattices using a combination of x-ray and neutron scattering techniques. For temperatures in the interval TN(Er)≤T≤TN(Ho) the Ho basal-plane order propagates coherently through the paramagnetic Er over a typical length scale of 1000 A. At low temperatures the Ho moments retain their bulk-like helical configuration, whereas the magnetic structure in the Er blocks has both basal-plane and c-axis components. Below TN(Er), the coherence length of the basal-plane order decreases on cooling, while the longitudinal component of the Er moments fails to order across the Ho block. It is argued that these results require an extension of current models of indirect exchange in superlattices to explicitly include the superlattice band structure.

Bi-2223 tapes were manufactured from a fine “two-powder” product produced by using an aerosol spray pyrolysis technique. Critical current density of 22000 A/ cm2 at 77K and 0 T was achieved. Nondestructive transmission x-ray diffraction study indicated good alignment of the superconducting grains. The texturing process of the superconducting phase was found to be nearly complete after the first 24 h of heat treatment for the samples studied. Pressing was found to play little role in the texturing process. The texturing can be enhanced by Ag-doping. Jc, however, was not found to be improved significantly, presumably due to the reduced effective cross-sectional area. A new phase, Bi-4435, was identified which may play a significant role in the formation of 2223.

We describe measurements of the magnetic critical fluctuations of holmium by x-ray scattering techniques. The x-ray results are compared to those obtained in neutron scattering experiments performed on the same sample.

The purpose of this CRADA was to characterize the structural properties of the superconductor material within the wires in order to determine which processing procedures produce the best superconductor texture and phase development, and hence the best ultimate current carrying capacity.

In this paper, we discuss changes in the phase diagram of hydrogen in both bilayer (i.e. 200–2000 Å Nb/ 100 Å Pd on glass) and multilayer configurations. In fact, it is the changes in this phase diagram, in addition to the Pd coating, that makes theses bilayer systems useful for hydrogen gas sensors. Comparison of x-ray diffraction, electrical resistivity and volumetric measurements of the films before and after hydrogen charging indicate that the phase equilibria between a correlated (high concentration) and a dilute phase of hydrogen in Nb is not sensitive to the number of layers in the films. On the other hand, the experimental methods show different behavior for 200 Å thick Nb films and thicker (>400 Å) Nb layers. Diffraction results showing unisotropic lattice expansion will also be discussed..

We review the results of recent neutron-scattering studies of the spin fluctuations in samples of La 1.89 Sr 0.11 CuO 4 which are ∼80% superconducting with T c = 10 K. The structure factor, S(Q), reflects three-dimensional modulated spin correlations with an in-plane correlation length of order 18 ± 6 A. The fluctuations evolve with temperature from being predominantly dynamic at high temperatures to mainly quasi-elastic (|ΔE| < 0.5 meV) at low temperatures. No significant differences are observed in the normal and superconducting states.

La 1.9 Ba 0.1 CuO 4 has been observed to undergo the following sequence of transformations upon cooling from 300 K: tetragonal (I4/mmm) equation orthorhombic (Cmca) equation tetragonal (P4 2 /ncm). The newly discovered low-temperature tetragonal structure can be understood geometrically as arising from a coherent superposition of the two domain modifications of the orthorhombic structure. Dynamically, it results from a second instability in the twofold degenerate soft modes of the high-temperature tetragonal phase. Energetically, the system can be modeled as an XY-spin system with temperature-dependent quartic anisotropy ν(T), and the low-temperature transformation coincides with an isotropic point ν(T 1 ) = 0. The relationship of the newly discovered transformation to other anomalous properties and to superconductivity is discussed briefly.