Study Of Magnetization Relaxation On Zone-Melted Yba2cu3o6+X Superconductors

The analytical magnetization versus time expressions for several flux-pinning models for high-Tc superconductors are deduced. Magnetic relaxation and hysteresis studies have been performed on a zone-melted YBa 2Cu3O6+x sample by SQUID. Nonlogarithmic magnetization decay is observed at relatively high temperatures; we attribute this to the nonlinear U(J) relationship which may arise from the local pinning potential Up(x), rather than collective pinning. At 70 K, the experimental data fits extremely well to the expression M(t)=M 0+a(T)ln ln(t/��) which is the result of the exponential U(J) relationship. Based on this U(J) law, the local pinning potential is determined to be Up(x)=U0(x/x0)[1-ln (x/x0). The voltage-current E(J) resulting from the observed U(J) relationship, as well as the role of the Y2BaCuO5 (211) phase in zone-melted YBCO is discussed. ? 1995 American Institute of Physics.