Scaling properties of the anisotropic critical current density in bulk textured YBaCuO. Evidence toward a 3D flux line lattice

Abstract

We have measured dc transport critical current densities of melt texture grown and magnetically melt textured bulk YBaCuO at 77 K and in magnetic field. A maximum value of over 31,000 A/cm2 is obtained with a field of 7 teslas applied parallel to the (a, b) planes. Over the rest of the angular range the critical current is shown to be determined mainly by thec-axis component of the applied field. Although this dependency is expected in the presence of two-dimensional vortices, in fact the data are shown to correspond better to the behavior expected of an anisotropic three-dimensional superconductor. These results are compared to magnetization measurements on the same samples. We show that when the field is directed close to the c-axis, superconducting transport currents flow at fields well above the field at which the irreversible magnetization disappears.