EXTRACTION OF ANISOTROPIC CRITICAL-CURRENT DENSITIES AND FLUX-PINNINGPOTENTIALS

Magnetic measurements were performed on an MTG YBa2Cu3O6+x sample at t hree field orientations. An extended Bean model was used to extract th e anisotropic critical current densities. Compared with the correspond ing magnetic measurement at the H parellel-to ab plane, the anomalous increase of calculated J(ab,ab) (critical current density flowing in t he ab plane at H perpendicular-to c-axis) with the applied field is mu ch more clear, and its field dependence is similar to that of magnetiz ation hysteresis at H parallel-to c-axis. Moreover, from the magnetiza tion relaxation measurements at H perpendicular-to ab the time depende nces of J(ab,ab) and J(c,ab) (critical currents flowing along the c-ax is at H perpendicular-to ab plane) were derived and used to determine the two corresponding effective activation energies for flux motion. B oth of the current density dependences can be fit with the power law b ut with different exponents, which may provide a possible explanation of the stronger temperature dependence of J(ab,ab) than J(c,ab).