S. Pace

Supercritical antisolvent precipitation: A new technique for preparing submicronic yttrium powders to improve YBCO superconductors

The solvent, supercritical antisolvent technique (SAS) has been used to produce submicronic particles of yttrium acetate for the synthesis of YBCO superconductors. For this purpose, in a continuous SAS apparatus dimethylsulfoxide (DMSO) as yttrium acetate solvent and supercritical carbon dioxide as antisolvent have been adopted. Experiments have been performed in the pressure range between 70 and 160 bar and for temperatures between 40 and 70 °C. Different concentrations of yttrium acetate in DMSO have also been tested. Various morphologies of yttrium acetate particles have been obtained, having mean particle diameters from 0.1 to 7 μm. At 40 °C and pressures larger than 120 bar, submicronic spherical particles of yttrium acetate of about 0.1 μm diameter and with a narrow particle size distribution have been achieved.

Phase stability for the in situ growth of Nd1+xBa2−xCu3Oy films using pulsed-laser deposition

We have determined the stability line in the 1/T−log[P(O2)] phase space for the synthesis of Nd1+xBa2−xCu3Oy (NdBCO) films. A systematic study of Tc, Jc, and ρ(T) dependence on oxygen partial pressure and temperature for the deposition of thin NdBCO films grown by pulsed-laser deposition was performed. The conditions for optimal NdBCO film growth were determined by varying oxygen partial pressure from 0.02 to 400 mTorr, and substrate temperature between 730 and 800 °C. The results show that the best NdBCO films are obtained at oxygen pressures in the range of 0.2–1.2 mTorr, depending on the substrate temperature. This is more than two orders-of-magnitude lower than the correspondent oxygen pressure appropriate for YBa2Cu3O7−δ film growth.

Magnetic relaxation of type-II superconductors in a mixed state of entrapped and shielded flux

The magnetic relaxation has been investigated in type-II superconductors when the initial magnetic state is realized with entrapped and shielded flux contemporarily. This flux state is produced by an inversion in the magnetic field ramp rate due to, for example, a magnetic field overshoot or undershoot. The investigation has been faced both numerically and by measuring the magnetic relaxation in BSCCO tapes. Numerical computations have been performed in the case of an infinite thick strip and of an infinite slab, showing a quickly relaxing magnetization in the first seconds. As verified experimentally, the effects of the overshoot (or the undershoot) cannot be neglected simply by cutting the first

Detection of the flux creep regime in the AC susceptibility curves by using higher harmonic response

10\char21{}100\phantom{\rule{0.3em}{0ex}}\mathrm{s}

Analysis of the capacitive coupling of Josephson transmission lines

in the magnetic relaxation. On the other hand, at very long times, the magnetic states relax toward those corresponding to field profiles with only shielded flux or only entrapped flux, depending on the amplitude of the field change with respect to the full penetration field of the considered superconducting samples. In addition, we have performed numerical simulations in order to reproduce the relaxation curves measured on the BSCCO(2223) tapes; this allowed us to interpret correctly also the first seconds of the

Influence of artificial pinning on vortex lattice instability in superconducting films

M(t)

Superconductivity in Sr2RuO4-Sr3Ru2O7 eutectic crystals

curves.

Vortex pinning properties in Fe-chalcogenides

In order to investigate the dynamic properties of the flux line lattice, the temperature dependencies of the basic and .

Vortex dynamics and pinning properties analysis of MgB2 bulk samples by ac susceptibility measurements

We study the capacitive coupling of two long Josephson junctions by imposing appropriate boundary conditions at the ends of the junctions. Numerical simulations show good agreement with analytical estimates of the parameter range for which reflections of fluxons at the coupled end of the junction occur. We discuss our results in terms of recent experiments concerning phase‐locking phenomena in Josephson junctions fluxon oscillators devices.

Irreversible low field flux penetration in sintered superconducting systems

In superconducting films under an applied dc current, we analyze experimentally and theoretically the influence of engineered pinning on the vortex velocity at which the flux-flow dissipation undergoes an abrupt transition from low to high resistance. We argue, based on a nonuniform distribution of vortex velocity in the sample, that in strongly disordered systems the mean critical vortex velocity for flux-flow instability (i) has a nonmonotonic dependence on magnetic field and (ii) decreases as the pinning strength is increased. These findings challenge the generally accepted microscopic model of Larkin and Ovchinnikov (1979 J. Low. Temp. Phys. 34 409) and all subsequent refinements of this model which ignore the presence of pinning centers.