MODELING THE FLUX CREEP CHARACTERISTICS OF HIGH-T_c SUPERCONDUCTORS

摘要

Barrier height for the flux creep increases with the temperature T, although the pinning potential is expected to decrease with increasing T. This anomaly was explained qualitatively by Welch by means of nonlinear potential barrier U( J) where the current J around which the analysis is centered decreases at high T and accordingly the nonlinearity leads to high pinning barrier energy at high T. To confirm this mechanism, U(J) relation of a wide range of J is required. By cooling a superconductor magnetized at higher temperature T_o + △T to an operating temperature T_o (High-Temperature Magnetization:HTM), low magnetization current J states equivalent to those after long-time creep are realized. The combination of the HTM method and the Hall voltage measurement attached to YBaCuO superconductor gives the magnetic relaxation curve in a wide range of J. These creep curves are analyzed in details with the simulation based on the creep equation. The observation-window is enlarged by HTM method and the nature of the current dependent pinning potentials is discussed.