Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Physics and Astronomy


Critical current density, J(,c), has been measured for Pb-^Ag(,1-x-y)Mn(,x)Al(,y)-Pb junctions over a wide range of temperature and^composition in order to determine the depairing effects of magnetic^impurities. Junctions, which are in a sandwich geometry typically 200^to 1000 nm thick, show well-defined diffraction patterns indicating^that the junctions are of high quality. The temperature dependence^of J(,c) for samples containing magnetic impurities are found to follow^a theory developed by Makeev et al. (1) for a bridge geometry. This^then implies that for the sandwich geometry, the modulus of the order^parameter at the boundary is proportional to its bulk value in the^superconductor as was assumd by Makeev et al. In this range, (xi)(,e) is^essentially independent of T, so this is a reasonable result. As T^approaches T(,c), J(,c) was found to be proportional to (I-T/T(,c))('2) as^predicted by the theories for the sandwich geometry. One junction^which had a Mn concentration of about 0.5% and a spin glass^temperature of 2.9K showed an inflection point in the J(,c)(' 1/2) vs. T data^near 2.7K. This change in slope may reflect a change in the spin^scattering rate as the temperature falls through the spin glasstemperature. If data are taken in the presence of a constantmagnetic field, then quantum oscillations are observed. These;oscillations arise from interference effect as successive quantized vortices enter the junctions; (1) A. I. Makeev, Y. N. Mitsai, and N. V. Shakhova, Sov. J. Low Temp. Phys. 6, 203 (1980).



Digital Repository @ Iowa State University,

Copyright Owner

Hong-Chang Yang



Proquest ID


File Format


File Size

87 pages