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Abstract

This thesis describes pSR observations of the internal magnetic field distribution n{B) as a function of temperature in LuNi₂B₂C (T[sub c] = 16.0 K, H[sub c2](0) = 7T), under a magnetic field of H = 1.2T applied parallel to the crystal c axis. The pSR polarisation signal is fitted to a nonlocal London model, assuming a square vortex lattice. By incorporating first order nonlocal corrections, this model achieves significantly better fits than the local London model. The fitted penetration depth temperature dependence λ(T) follows the form expected for a BCS s-wave superconductor, although the dependence is also consistent with a slight linear increase in the penetration depth λ with rising temperature. The rate of any such linear growth, however, is smaller than would be expected for an energy gap Δ with line nodes. The fitted core radius temperature dependence p(T) reveals a Kramer-Pesch effect, or linear contraction of the vortex core radius p upon cooling at low temperatures T