Evaluation of the Critical Current Density of Multifilamentary ${\rm Nb}_{3}{\rm Sn}$ Wires From Magnetization Measurements

A simple model for evaluating the critical current density of multifilamentary wires from magnetization measurements was examined. This model assumes that each sub-element is in good approximation a superconducting hollow cylinder, which limits its validity to powder-in-tube wires and wires whose filaments are completely merged within the sub-elements. The magnetic moment of short samples of four wire types was measured in a SQUID magnetometer at applied fields of up to 7 T in the temperature range from 4.2 to 15 K. The evaluation model discussed in this work was used to obtain critical current densities from the results of these measurements. The calculated values were compared to transport measurement results, and satisfactory agreement was found between the two data sets. Furthermore, it was shown by means of magnetization measurements of individual sub-elements that the coupling between the sub-elements in the wire samples has a negligible effect on such measurements.