Comparison of flux pinning in single crystals and melt-textured YBa2Cu3O7-x

Flux pinning properties of single crystals and melt-textured samples of YBa2Cu3O7-x were studied for external magnetic field oriented parallel and perpendicular to the CuO2 planes (ab-planes). For H parallel to ab vortex behaviour is mainly determined by a very effective intrinsic pinning mechanism. The irreversibility line is located in the region of higher fields and temperatures in comparison with the irreversibility line for H perpendicular to ab. In a single crystal for H perpendicular to ab, we observed an increase in the critical current density je with magnetic field - the so-called "fishtail effect" - in a very broad temperature range. For H parallel to ab, this effect is observed only at temperatures close to T-c, when the intrinsic pinning is much weaker.