  The Abricosov vortex and bundles dynamics was experimentally investigated in
Earth's magnetic field range. Isothermal relaxation features in YBCO single
crystal samples with strong pinning centers were studied for different
sample-field orientation. The normalized relaxation rate S obtained allowed to
estimate the effective pinning potential U in the bulk of the YBCO sample and
its temperature dependence, as well as the critical current density Jc. A
comparison between the data obtained and the results for similar measurements
in significantly higher magnetic fields was performed. To compare different Jc
measuring techniques magnetization loop M(H) measurements, were made. These
measurements provide many important parameters of the sample under study
(penetration field Hp, first critical field Hc1, etc.) that contain the
geometrical configuration of the samples.
