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|Title:||Three-Dimensional Magnetic Dopant Atoms in Transition-Metal Superconductors: Part I. Localized Magnetic Moments on Chromium and Manganese Dopant Atoms in Niobium and Vanadium. Part Ii. The Effects Ofchromium and Manganese Dopant Atoms on The Upper Critical Magnetic Field of Niobium (Squid)|
|Department / Program:||Physics|
|Degree Granting Institution:||University of Illinois at Urbana-Champaign|
|Subject(s):||Physics, Condensed Matter|
|Abstract:||This thesis consists of two parts. The first part deals with the question of whether localized magnetic moments are present on the 3d atoms, Cr and Mn, when dilutely doped in Nb and V. The second part deals with the pair-breaking effects of Cr and Mn dopant atoms on the upper critical magnetic field of Nb.
In Part I we review the experimental situation regarding the presence of localized magnetic moments on 3d dopant atoms in transition-metal superconductors, and briefly describe the salient features of some traditional theories of localized moments in metals. We indicate why the magnetic behavior of the host-metal ions may be significant in the case of transition-metal hosts, and we present a simple model in which we include the effects of host-metal magnetism. We then give an account of magnetic susceptibility measurements on films of Nb and V, pure and doped with Cr and Mn. We discuss the data in terms of our model. Our results indicate the presence of localized magnetic moments on Cr and Mn dopant atoms in both Nb and V.
In Part II we briefly review the theories of magnetically doped superconductors. We then give an account of measurements of the superconducting transition temperature, T(,c), and of the upper critical magnetic field, H(,c2)(T), of several Nb films, pure and doped with Cr and Mn. We relate the superconducting properties of these films to various normal-state material parameters, and we discuss the implications of these relations on the superconductivity of Nb. We find that T(,c) of Nb is decreased in the presence of Cr or Mn, by amounts that are consistent with the existence of localized moments. Our results for H(,c2)(T) indicate, for both Cr and Mn dopants in Nb, that the pair-breaking effect of the magnetic dopants is additive with the pair-breaking effect of the applied magnetic field, and is possibly temperature-independent.
Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 1984.
|Date Available in IDEALS:||2015-05-13|