Differential Paramagnetic Effect in Superconductors

The magnetic moment and the differential magnetic susceptibility of two spherical samples of tin and tantalum have been measured as a function of magnetic field and temperature. The differential paramagnetic effect (DPE) is observed in both ac and dc mutual inductance measurements provided the sample exhibits a good Meissner effect. For a superconducting sample in which the infinite conductivity behavior dominates the Meissner effect, the DPE does not appear in the ac measurements but does, under certain conditions, show up in dc measurements. The results of the dc mutual inductance measurements are used to classify the DPE as reproducible or nonreproducible. The former is characteristic of ideal Meissner-type superconductors while the latter is more characteristic of superconductors whose macroscopic magnetic properties are dominated by the classical infinite electrical conductivity behavior. The superconducting-to-normal transitions obtained by the three techniques are compared and the data discussed in view of (a) occurrence of the DPE; (b) magnitude of the DPE; (c) ability of these data to give information about the volume participation of the sample; and (d) relation of the "characteristic magnetic fields" determined by these transitions and the bulk critical field of the sample.