SCALING PROPERTIES OF THE ANISOTROPIC CRITICAL-CURRENT DENSITY IN BULK TEXTURED YBACUO - EVIDENCE TOWARD A 3D FLUX-LINE-LATTICE

We have measured dc transport critical current densities of melt textu re grown and magnetically melt textured bulk YBaCuO at 77 K and in mag netic field. A maximum value of over 31,000 A/cm2 is obtained with a f ield 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 ma inly by the c-axis component of the applied field. Although this depen dency is expected in the presence of two-dimensional vortices, in fact the data are shown to correspond better to the behavior expected of a n anisotropic three-dimensional superconductor. These results are comp ared to magnetization measurements on the same samples. We show that w hen the field is directed close to the c-axis, superconducting transpo rt currents flow at fields well above the field at which the irreversi ble magnetization disappears.