Nonideal Behavior of Inhomogeneous Superconducting Alloys

Abstract

An investigation of nonideal superconducting properties of inhomogeneous tin alloys reveals that the behavior of such samples represents a diverse set of phenomena intimately related to the nature of the inhomogeneities. Resistive temperature and field transitions are presented along with critical field data, magnetization curves, and remnant moment measurements. Several inhomogeneous samples are shown to possess very unstable magnetization curves and to show flux penetration at fields less than the bulk critical value. Annealing can make the magnetization more or less ideal, or produce very little change, depending on the nature of the inhomogeneity and the way it is altered in the process. Annealing sharpens the resistive transition temperature curve when more impurity goes into solution. It also can produce a large change in the apparent transition temperature. Samples examined represent both positive and negative surface energy materials containing either predominantly normal state or superconducting state inhomogeneities, or a combination of both. Although negative surface energy materials show more hysteresis than positive surface energy materials under equivalent conditions, the nature of the inhomogeneity and its role in flux retention is more important than the simple difference between positive and negative surface energy. A detailed description of the behavior of each sample and speculations as to the origins of features not heretofore reported are included.