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We have performed measurements of the magnetic field dependence of the critical current density J/sub c/ of Bi-2212/Ag round wire produced by isothermal melt processing. In contrast to the case for flat tape, there is very little dependence of J/sub c/ on on the direction of the magnetic field as it is rotated normal to the wire axis which is the direction of the nominal current flow. However, when the angle of the magnetic field direction is rotated from normal to the wire axis to parallel to that axis, J/sub c/ at 64 K and 0.2 T increases by more than a factor of four. Again, this is in contrast to the results observed for Bi-2212/Ag and Bi-2223/Ag flat tapes, which show no anisotropy under similar experimental conditions. We can explain these differences in angular anisotropy by referring to the microstructure of these two conductor types, which have distinctly different types of grain alignment. We discuss the general behaviour of the dependence of J/sub c/ on the orientation of a magnetic field for high temperature superconductors. [ABSTRACT FROM PUBLISHER]

Examines the measurement of the anisotropic properties of Bi2223/Ag tapes with and without the silver sheath. Relationship between the resistivity anisotropy ratio and rolling plane; Use of the standard four-probe method in measuring anisotropic transport properties; Description of critical current scaling as a function of the angle theta.

Investigates ab-plane anisotropy of the critical currents in twinned YBa[sub 2]Cu[sub 3]O[sub 7-delta] superconductor films. Deposition of films on crystalline yttria-stabilized zirconia (YSZ); Effect of the alignment of the twin boundary mosaic diagonal; Nucleation of the YSZ buffer layer in large grains.

We argue that superconductor/ferromagnet multilayers of nanoscale period should exhibit strong pinning of vortices by the magnetic domain structure in magnetic fields below the coercive field when ferromagnetic layers exhibit strong perpendicular magnetic anisotropy. The estimated maximum magnetic pinning energy for single vortex in such a system is about 100 times larger than the pinning energy by columnar defects. This pinning energy may provide critical currents as high as 10[sup 6]-10[sup 7] A/cm[sup 2] at high temperatures (but not very close to T[sub c]) at least in magnetic fields below 0.1 T. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We use interlayer intrinsic tunneling resistivity to probe the pseudogap in Bi2Sr2CaCu2O8+y in magnetic fields up to 60 T. A map of the field–temperature (H–T) diagram of the pseudogap state reveals the pseudogap as a dominant feature up to very high levels of hole doping. The unconventionally large quantum fluctuation regime observed on the overdoped side is consistent with the pseudogap in the vortex cores. Unlike the characteristic fields of the superconducting state, the field that closes the pseudogap at low temperatures is temperature-independent. It is related to the pseudogap temperature T★ through a simple Zeeman energy scale, pointing to the pseudogap controlled by the spin rather than the orbital degrees of freedom. [Copyright &y& Elsevier]

A dense sample of MgB2 (Tc=38.5 K) was synthesized under 200 MPa pressure using a novel hot isostatic pressing (HIPing) technique, and a high-purity single crystal of YBa2Cu3O7−δ (Tc=93.5 K) was grown in a home-made BaZrO3 crucible. Electric field vs current density (E–J) isotherms of the MgB2 and YBa2Cu3O7−δ high-temperature superconductors were measured and analyzed in terms of the critical scaling model. E–J isotherm sets were taken at fields ranging from 2 to 90 kOe. Scaling and resistivity data reveal a smooth transition from a vortex glass to a vortex liquid state for the bulk MgB2 sample and the existence of both a vortex lattice melting line and a vortex glass to vortex liquid line in the YBa2Cu3O7−δ single crystal. The critical scaling exponents for both systems are presented. A more complete (H–T) phase diagram, containing the upper critical field Hc2(T), the vortex-glass transition line Hg(T), and the magnetic irreversibility line Hirr(T) was established for bulk MgB2. [Copyright &y& Elsevier]

From the c-axis interlayer resistivity measurements in a field up to 60 T, we evaluate the pseudogap closing field Hpg at which the low-energy density of state is restored to its ungapped value. We find that Hpg becomes temperature independent at low temperatures, in contrast to the characteristic fields of the superconducting state. The Zeeman energy of Hpg is scaled by the pseudogap temperature, indicating a predominant role of spins over the orbital effects in the formation of the pseudogap. [Copyright &y& Elsevier]