Dynamics of trapped magnetic fluxes in single-crystal YBCO in weak fields.

The dynamics of low-density trapped magnetic fluxes, including local fluxes, are investigated in single-crystal YBCO in the region of strong thermal fluctuations near the superconducting phase transition. A substantial difference of the isothermal magnetization-relaxation behavior from the quasi-logarithmic behavior observed earlier in strong magnetic fields is established for the first time. The effective pinning potential in the temperature interval close to the critical temperature is estimated in terms of the simplest model of thermally activated creep. [ABSTRACT FROM AUTHOR]