Studies of non-ideal superconductors using DC magnetic methods

Among the most informative and facile methods for investigations of a superconductor are measurements of its static magnetization. The objective of this paper is to analyze some experimental features frequently observed in static (dc) magnetization studies of conventional and high-(Tc) superconductors. We shall discuss investigations employing measurement protocols in which the sample is cooled through the superconductive transition temperature in a finite magnetic field ('field cooled') and compare this with zero-field-cooled studies. Also considered are reversible and irreversible materials; particle size effects; some effects of granular and multiply-connected materials; penetration depth studies of type 2 materials in the vortex state; and fine scale 'multi-connected' materials produced by heavy ion irradiation that produces very significant enhancements of the critical current density J(sub c) in the high temperature superconductor YBa2Cu3O7. Many of these superconductors are 'non-ideal' in that they may contain defects and inhomogeneities or may have small dimensions comparable with microscopic superconductive lengths. Practically speaking, however, such materials are often encountered experimentally and can have very desirable physical properties, such as high J(sub c) values in the ion-irradiated crystal.