Direct relationship between trapped magnetic flux characteristics and percolation transition temperature in a practical sized bulk high-temperature superconductor

Abstract

The trapped magnetic flux characteristics of a Gd-system bulk high-T c superconductor (HTS) near the so-called percolation transition temperature was investigated experimentally. The percolation transition temperature was directly determined from the temperature dependence of the E-J characteristics with a bar-shaped HTS. Next, the disc-shaped bulk HTS sample was magnetized by means of a field-cooling process, and then the decay of the trapped magnetic flux density was monitored for 30 min after the exciting current of the electromagnet was cut off. It was shown that the decay rate of trapped magnetic flux changed considerably around the percolation transition temperature. Furthermore, the trapped flux showed stepwise decay, and these phenomena could explain the percolation mechanism of the depinning process. From our study, the percolation temperature may be utilized for the limit parameter in order to design application systems with a practical sized bulk HTS.