Proximity Effects between Superconducting and Magnetic Films

Abstract

Superimposed normal-superconducting films can be used in conjunction with theory to investigate the nature and magnitude of the electron-electron interaction taking place in the normal metal. We report studies in which the normal metals were various types of magnetic materials: the ferromagnets Fe, Ni, and Gd; antiferromagnetic Cr; and the dilute magnetic alloys 1% Fe in Mo and 2.9% Gd in Pb (the last actually being a low-transition-temperature superconductor). The superconducting metal in all cases was pure Pb. Measurements of the transition temperature of the sandwich as a function of Pb film thickness were compared with a combined theory incorporating the de Gennes-Werthamer calculation of the proximity effect in nonmagnetic materials together with the Abrikosov-Gor'kov model of superconductivity in dilute magnetic alloys. Agreement for the alloy systems was satisfactory with no adjustable parameters, while extension of the theory to the concentrated, ordered systems with one parameter adjusted was qualitatively reasonable. Certain aspects of superimposed films in general were also studied: Diffusion of one metal into the other during and after deposition; dependence of the sandwich transition temperature on the order of deposition of the component films; recrystallization at room temperature; and interfacial cell reactions, selectively oxidizing one of the components at room temperature in ambient atmosphere.