Minor Magnetization and Flux Creep Characteristics in YBaCuO Superconductors with Distributed Pinning Forces

Abstract

Magnetizaion and flux creep characteristics were measured in bulk samples of YBaCuO superconductors with (Y-55) and without (Y-25) doping of Ag2O and 211 phases. Magnetization in a minor loop showed systematic deviations from the critical state model. Minor magnetization modified to hold a distribution of critical current densities agrees quite well with the observed curves. The distribution of critical current densities Jc is given by a triangular type with an averaged \( \bar J_c \) and a distribution width ΔJc. The sample Y-25 showed that Jc distribution changed with temperatures T and applied magnetic fields Bo. In the sample Y-55, however, the pinning force distribution was nearly independent of T and Bo. Flux creep characteristics with nonlinear logarithmic time dependence were observed in the sample Y-25 and discussed using the Jc distributions.