An experimental investigation of the magnetization of superconductors

• Main Author: McEvoy, Joseph Peter
• Published: Imperial College London 1968
• Subjects: 530.4
• Online Access: https://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.623090

This dissertation describes magnetization experiments on various superconducting metals and alloys. Primarily, the intent of the research was to measure and explain the effect of the surface sheath on the magnetic properties of bulk material under quasi-ideal conditions. Extensive measurements have been carried out on lead (Pb), tantalum (Ta), dilute lead-bismuth (Pb-Bi) alloys and dilute tantalum- niobium (TaNb) alloys. All the samples were monocrystalline rods with carefully prepared and examined surfaces. Some preliminary results were also obtained on polycrystalline lead-bismuth (PbBi) alloys. Surface condition is crucial to an investigation of the properties of the surface sheath. For example, it has been established that a dense layer of dislocations exists on the surface of "as grown" electron-zone-refined tantalum rods. This produces a high K (short electronic mean free path) skin thicker than the coherence length which must be removed by electropolishing before meaningful (i.e. characteristic of the bulk) measurements can be made. Similar but less-understood effects occur in lead (Pb). The formation of oxide layers on the surface of well-polished lean (Pb) crystals slightly increases the surface nucleation field presumably due to changes in the nature of the electron scattering at the metal/vacuum boundary.