INVESTIGATION OF CRITICAL-STATE IN MELT-PROCESSED YBA2CU3O7-DELTA THICK-FILMS

The magnetic moment of square planar melt processed YBa2Cu3O7-delta th ick films is observed to scale with the cube of the sample width at 4. 2 K, suggesting that current flow on the length scale of the film dete rmines its magnetization at this temperature. A well-defined discontin uity in slope in the scaling data at a sample width corresponding to t he average grain size (almost-equal-to 2 mm) implies the coexistence o f distinct intra- and inter-grain critical current densities of 1.1 x 10(5) A cm-2 and 0.4 x 10(5) A cm-2 at 1 T and 4.2 K. The presence of a critical state in the films at 4.2 T is confirmed by removing the ce ntral section from a specimen. The observed change in magnetic moment is in excellent agreement with theory for fields greater than almost-e qual-to 2 T. A critical state is not observed at 77 K which suggests t hat the grains are only weakly coupled at the higher temperature.