Pinning features of magnetic flux trapped by YBCO single crystals in weak dc fields

The dynamics of Abrikosov vortices and bundles was experimentally investigated in Earth magnetic field range. Isothermal relaxation features in YBCO single crystal samples with strong pinning centers were studied for different sample-field orientation. The obtained values of normalized relaxation rate S allowed us 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 provided many important parameters of the samples under study (penetration field Hp, first critical field Hc1, etc.) that involve the geometrical configuration of the samples.