Single vortex creep in Tl2Ba2CaCu2O8 epitaxial thin films.

Abstract

By measuring the magnetization hysteresis loops and the remanent magnetization relaxation for an epitaxial ${\mathrm{Tl}}_{2}$${\mathrm{Ba}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8}$ thin film, we determined the temperature dependence of the experimental critical current density j(T) and the normalized relaxation rate S(T) at ${\mathit{B}}_{\mathit{e}}$=0.4 T. It is shown that the data j(T) and S(T) can be well fitted to the single vortex creep model with only one fitting parameter in each fitting process. The data j(T) and S(T) were then used as the input for the generalized inversion scheme (GIS); the output of the GIS, i.e., the temperature dependence of the true (unrelaxed) critical current density ${\mathit{j}}_{\mathit{c}}$(T) and the pinning potential ${\mathit{U}}_{\mathit{c}}$(T), follows the theoretical expressions predicted by the single-vortex collective pinning model. Finally, the magnetization (and thus the current) dependence of the activation energy U(${\mathit{M}}_{\mathit{T}=0}$, T=0) was determined by using the magnetization relaxation data. Again, the single vortex creep model explains the resulting U(${\mathit{M}}_{\mathit{T}=0}$, T=0 K) relation very well. \textcopyright{} 1996 The American Physical Society.