Magnetic characterization on the melt processed YBa 2Cu 3O 7 and Bi 1.8Pb 0.2Sr 2CaCu 2O x superconductors

Abstract

Field and temperature dependence of the magnetization, remanent magnetic moment relaxation and AC susceptibility studies have been performed for the quench and melt growth (at different solidification speeds) processed YBa 2Cu 3O 7 (123) species with different microstructures, and for the Bi 1.8Pb 0.2Sr 2CaCu 2O 8 sample, prepared by crystallization from the glass. The Bi-containing superconductor reveals granular behavior with intragrain J c ∼ 10 6 A/cm 2 and intergrain J c ∼ 10 3 A/cm 2 at 4.5 K with possible enhanced critical current density in grain agglomerations. YBa 2Cu 3O 7 samples exhibit a weak link free character with a magnetically estimated J c of about 10 5 A/cm 2 at 10 K and 10 3–10 4 A/cm 2 at 77 K. Peculiarities in magnetization loops and AC susceptibility curves have been attributed to the contributions to the magnetic response from the superconducting areas with different extensions. The temperature behavior of the flux creep activation energy is consistent with the assumption that in the Bi-containing superconductor there is a large amount of pinning centers with only a low pinning potential, while in the 123 material there is a wide distribution in the pinning energy. The highest J c and pinning characteristics have been obtained for an YBa 2Cu 3O 7 sample, prepared using the highest 123 phase crystallization speed (100 K/h).