Non-contact determination of critical current densities in a superconducting YBa2Cu3Oy cylinder

Abstract The determination of the critical current density ( j c ) of a superconducting ceramic is a vital part of the assessment of its suitability for electrical and electronic applications. However, in bulk materials where the current carrying capacity of a test specimen is typically several amps, great care is required in the preparation of low resistance current contacts if heating effects are to be eliminated. Several groups have therefore developed non-contact techniques for the determination of j c which rely on the measurement of the hysteretic magnetisation loop of a material in an external applied magnetic field. However, one difficulty with such measurements is the need to identify separately the contribution to the magnetisation due to intra-granular currents (i.e. circulating currents which do not cross grain boundaries) from that due to inter-granular currents (i.e., bulk currents which flow between grains); the critical current densities in the former being typically several orders of magnitude larger than the latter. For the assessment of the transport properties of bulk materials only the intergranular critical currents are of practical importance. Here we present an extension of the basic technique which reduces the effects of intra-granular magnetisation and eliminates the effects of the dependence of the critical current density on the external magnetic field.