Magnetic Properties of Superconducting Lead-Base Alloys

Magnetization measurements have been made at 4. 2^ on a variety of binary lead-base alloys, with the purpose of determining the effects of solutes, precipitates, and dislocations on superconducting properties. Increasing solute concentration results in increasingly broad magnetic transitions, the results correlating with normal-state electron mean free path in quantitative agreement with "negative surface energy" theories of Abrikosov and others. Magnetic hysteresis and trapped flux are small for annealed single-phase specimens, but are greatly increased by plastic deformation and by cellular precipitation. The maximum magnetic field to which superconductivity persists in these alloys is apparently determined by the electron mean free path, whereas extended defects such as dislocations and precipitates are primarily responsible for magnetic hysteresis and trapped flux.