CRITICAL CURRENT-DENSITY IN SINTERED YBA2CU3O7-Y - A COMPARISON BETWEEN DIFFERENT KINDS OF MEASUREMENTS AND PROBLEMS IN THEIR INTERPRETATION

The authors report the results of critical current density measurements in sintered YBa2Cu3O7-y samples using different methods and interpretive models. Their aim is to describe the problems encountered when measuring intergranular critical current density, especially at low magnetic field values. These problems are due to the fact that J c is strongly dependent on the magnetic field and the measuring methods in common use generally imply a non-uniform magnetic field value inside the sample. Under these conditions, measurements of Jc do not reflect a real value but a mean value which is heavily dependent on the form and dimensions of the sample. This makes it impossible to compare directly readings made on different samples. The authors suggest to interpret magnetization readings with a numerical simulation based on the 'critical state' model. They also offer an analysis of the signal induced in the sample as the best inductive method of measuring Jc irrespective of the shape or dimensions of the sample, within limits that they specify. They also consider the effects of clusters and the problems they cause in measuring Jc in samples where they are present.