This thesis describes investigations into the superconducting and magnetic properties of the rare earth nickel borocarbides, RNi2B2C. In chapter 1 the field of study is introduced and the basic properties of the materials described. Key theoretical concepts in superconductivity and properties of a vortex lattice are discussed in chapter 2. Chapter 3 describes how crystals are grown and characterised in the laboratory. The theoretical background and experimental techniques used in neutron scattering, the principal tool used in the experiments, are given in chapter 4. An investigation into the magnetic field distribution around vortices through the form factor ratio, F II/F \0, in the non-magnetic compounds Y - and LuNbB2C, is detailed in chapter 5. It is found that the current theoretical approaches do not provide a good description of this field distribution. Chapter 6 consists of an enquiry into the magnetic structures formed in ErNbB2C both with and without the application of a magnetic field. In zero field the development of a ferromagnetic component at low temperatures is analysed. The response to a magnetic field applied along three distinct crystallographic directions reveals more complicated behaviour than anticipated, including superlattice behaviour in the vicinity of the superconducting upper critical field for two of the orientations. Finally, a survey of the properties of the vortex lattice with applied field and temperature in ErNbB2C is presented in chapter 7. The 90° reorientation of the rhombic lattice at a critical field HI and the square-to-rhombic symmetry transition at H2 are investigated. The development of magnetic order is found to have a dramatic impact on the vortex lattice in this material. The principal results arising from this thesis are summarised in chapter 8.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:269053 |
| Date | January 2002 |
| Creators | Bancroft, Nicola Juliette |
| Publisher | University of Warwick |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://wrap.warwick.ac.uk/88010/ |
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