Superconductivity as a Structural Characterization Tool in Amorphous Materials

Abstract

This thesis presents the use of superconductivity as a structural probe for studying amorphous and metastable materials. The characteristics of the superconducting state which facilitate its use as a probe are explained, followed by a description of some of the properties of the materials studied. The superconducting measurements performed were critical current, transition temperature and upper critical field. Materials prepared by rapid quench from the melt, sputter deposition and ion beam mixing were studied. The critical current measurements performed on liquid quenched materials reflect three pinning mechanisms. Crystalline inclusions in otherwise amorphous (Mo0.6Ru0.4)80Si10B10 produced a dramatic increase in critical current. The pinning in purely amorphous (Mo0.6Ru0.4)82B18 was shown to be affected by pinning by surface roughness on the sample edges. This contribution can be eliminated by a proper sample geometry and electropolish treatment. The bulk pinning in purely amorphous (Mo0.6Ru0.4)82B18 was shown to first decrease and then increase as a function of annealing time. This reflects the disappearance of quenched in inhomogeneous strains and excess volume defects followed by the growth of an inhomogeneity such as compositional phase segregation during an anneal. The upper critical field was measured for liquid quenched (Mo0.6Ru0.4)1-xBx for x = 0.12, 0.18 and 0.22 both before and after an anneal. The annealed samples exhibited greater transition widths and more curvature in the Hc2(T) curves than the unannealed samples which are evidence for a growth of inhomogeneities upon annealing. Measurements on sputter deposited (Mo0.6Ru0.4)82B18 were performed on samples sputtered in low (5 µm) and high (75 µm) Ar pressure, The material sputtered in low Ar pressure had a greater drop in Tc than the liquid quenched material and a pinning profile which exhibited a peak near Hc2. The sample sputtered in high Ar pressure was very inhomogeneous as evidenced by transition width and flux pinning force profile. Measurements were performed on ion beam mixed Mo55Ru45. The structure consisted of an amorphous matrix with crystalline inclusions. The pinning profile was characteristic of a strong pinning mechanism. The pinning force decreased then increased as a function of ion beam dose. This reflects the destruction of the remnants of the original structure followed by the formation of an inhomogeneity such as σ-MoRu or Xe gas bubbles during ion beam irradiation.