Measurements of intergranular critical current density of high Tc sintered superconductors

It's well known that the intergranular critical current density (Jc) depends largely on the magnetic field value because of the presence of weak links between the grains in sintered samples. This strong dependence determines some problems in Jc measurements, above all at low magnetic fields value where such dependence is even more marked. In particular: supercurrents create a self-field which may affect the uniformity of Jc values. In these conditions the measurement evidently gives a mean value of Jc, depending on the size of the sample. For magnetic field values of only a few hundred Gauss, Jc values are already so low that a high degree of measuring sensitivity is required. Lastly it is difficult to distinguish homogeneous from inhomogeneous (clusters) samples by means of ordinary inductive measurements. The aim of this paper is to propose a method of measuring intergranular critical current density which overcomes these problems