  An experimental study of low density captured magnetic flux dynamics in YBCO
single crystal samples near the superconducting phase transition point has been
performed. Vortex dynamics similar to thermally assisted flux flow regime
(TAFF) has been observed for the first time in such weak fields. It will be
shown that Zeldov's thermoactivated creep model successfully describes the
behavior of the magnetization in the YBCO single crystals in our experiments.
Within the framework of this model the estimation of normalized relaxation rate
was made.
