A. J. Batista-Leyva

The resistive transition of (Hg0.85Re0.15)(Ba1-ySry)2Ca2Cu3O8+δ superconducting polycrystals

The resistive transition of (Hg0:85Re0:15)(Ba1� ySry)2Ca2Cu3O8þd superconducting polycrystals, with y ¼ 0:00, 0.17, 0.20 and 0.28 has been experimentally studied at different magnetic fields ( 6 500 Oe), being the Arrhenius plot char- acterized by two linear regions with different slope in the resistive tail. The crossover temperature between them depends on the Sr content. The dependence of the intergranular pinning energy with the magnetic field, for both regions, follows a power law, being the exponent dependent on the Sr content in a non-linear way. The intergranular irreversibility line benefits from the Sr doping, associated with the improvement of the transport properties (even in the normalstate) with the increment of Sr. The contribution of fluctuations to the conductivity is calculated from the measurement of re- sistivity in the interval of 130-300 K, and the interlayer coupling energy is obtained. From these calculations, an es- timation has been made of the interlayer distance, finding an increment with Sr content. Our study suggests that the Sr can improve the performance of Hg-based HTc polycrystals for transport applications, which are basically determined by intergranular properties. 2002 Elsevier Science B.V. All rights reserved.

Magnetic irreversibility in (Hg1−xRex)Ba2Ca2Cu3O8+δ: effects of neutron irradiation

Abstract We studied the intragrain magnetic hysteresis of the superconductor (Hg 1− x Re x )Ba 2 Ca 2 Cu 3 O 8+ δ ( x =0.10, 0.18 and 0.25) close to T c . From the magnetization curves we determined the temperature dependence of the irreversibility field ( H irr ( T )), and the field dependence of the magnetization curve width ( ΔM ( H )). After irradiation to a fluence of 2×10 21 m −2 ( E >0.1 MeV), the magnetization curves moderately increase their symmetry, and sizeable enhancements of H irr ( T ) and ΔM ( H ) are observed. Although the substitution x =0.18 shows the best pinning properties before irradiation, x =0.10 matches—or even surpasses—them afterwards. This suggests that, within our temperature and field window, neutron irradiation plays a far more important role than Re-substitution in enhancing the irreversible behavior in the Hg-1223 system.

Relaxation of the transport critical current in deoxygenated YBa2Cu3O7−δ

Abstract We present a study of the transport critical current relaxation for a set of carefully deoxygenated YBa2Cu3O7−δ polycrystalline samples, in such a way that the oxygen losses mostly come from the intergrain region, while the grains remain essentially unchanged. The dependence of the relaxation rates on the maximum magnetic fields applied to the sample, in the remanent state, is consistent with the predictions of a phenomenological model, in which the thermally activated relaxation of the intragrain magnetization provokes a time decay of the intergrain local fields, thus producing a temporal increase of the transport critical current.