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Design aspects of a differential magnetic susceptometer for high temperature superconductors

The design of an ac magnetic induction susceptometer is described and results given for bulk YBCO samples in parallel and perpendicular applied fields and thin film YBCO samples in perpendicular applied fields. The susceptometer employs a double-differential technique designed to accept bulk or thin film samples mounted parallel or perpendicular to the applied field. Theoretical details are given regarding the particular methods used to calculate the complex external and internal susceptibility, flux density and magnetization and the validity of the quadrature detection technique. Performance details of the susceptometer are provided regarding the system sensitivity for frequencies 20, 50 and 100 Hz. Complex susceptibility results are given as a function of applied field magnitude and frequency for the various specimens analysed. The results obtained are compared with Bean plate theory and the critical currents for intergranular and intragranular regions are determined.