  In this paper we present our results on the low density magnetic flux pinning
characteristics, obtained though HTSC samples magnetization relaxation
measurements M(t) near the phase transition temperatures (0,8 < T/Tc > 0,99).As
the main object of investigation we have chosen pure YBa2Cu3O7-x (YBCO) single
crystal samples with optimal oxygen saturation. We note the presence of strong
pinning in the system of unidirectional planar defects and a significant
nonmonotonicity of the Up(T) dependence behavior for low density trapped
magnetic flux.
