Abstract
Magnetization as a function of applied magnetic field has been measured at 4.2°K for binary solid solution alloys of In, Tl, Sn, Hg, Na, and Bi in Pb. For pure Pb, superconductivity is destroyed when the field penetrates abruptly at the thermodynamic critical field HC. With sufficient alloying element in solution, the field, instead, first penetrates at HFP(<HC) and penetrates gradually, full penetration and destruction of superconductivity not being reached until HN (>HC). Increasing solute concentration decreases HFP and increases HN in a manner predicted by the ``negative surface energy'' theories of Abrikosov and others. Annealed specimens approach reversible magnetic behavior and exhibit little trapped flux. Plastic deformation is found to increase HFP, the area under the ascending magnetization curves, the hysteresis, and the trapped flux, but has little effect on HN. The results indicate that the high critical field of these alloys results from the lowered surface energy of a superconducting-normal interface and not from any specific filamentary features of the microstructure. Dislocations do, however, increase the magnetic hysteresis and, it is inferred, the current-carrying capacity of these alloys.
Published Version
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