Magnetic Impurity Scattering in in Situ Superconductors

摘要

Measurements of ac losses for in situ prepared superconducting composites consistently show loss values higher than those observed for bronze process materials. To get the measured ac loss one needs an effective filament size in the range of 20 to 50 mu m. Our goal in this work is to understand quantitatively the origin of this coupling between filaments and to develop methods for controlling it. To reduce the ac losses it is desirable to reduce the cross linking of filaments and the proximity coupling through the Cu. This should not reduce J/sub c/ because in all cases J/sub c/ is controlled by pinning of the flux line lattice by either grain boundaries or superconductor-Cu boundaries. In fact, J/sub c/ vs H curves are essentially the same as for continuous filament materials. There is no evidence that a breakdown of the proximity coupling in the Cu controls J/sub c/ and there seems to be more than adequate filament-filament coupling. Therefore the goal is to reduce this filament-filament coupling, both cross joining and proximity coupling. The first step in this is to control proximity coupling by the introduction of magnetic impurities into the normal metal barrier. Presented here are the results of a study of the model system Pb-(AgMn)-Pb to understand all of the basic physics involved and to learn quantitatively the effects of magnetic impurity scattering in the N layer. Because both magnetic and non-magnetic scattering will be important in the Cu-Nb sub 3 Sn systems we add both Mn and Al to the Ag to determine the effects of both the magnetic scattering rate (pi/sub s/ exp -1 ) and non-magnetic scattering rate (pi/sub N/ exp -1 ). (ERA citation 09:031391)