Andrew Boothroyd

Abstract:

The reflectometer CRISP at ISIS is being upgraded to expand its capabilities in the polarised-beam mode. The polarisers are being replaced by Fe-Co-V:TiNx supermirrors to give a higher incident flux and a two-times larger dynamic range. The flippers have also been redesigned to give higher flipping efficiencies over larger beam sizes and wavelength ranges. The improvements are described and compared to the current instrument performance. (C) 1998 Elsevier Science B.V. All rights reserved.

Abstract:

We have applied the technique of polarised neutron reflectometry (PNR) to investigate the magnetic held penetration in different superconducting phases of Nb, namely the Meissner state (H < H-c1), the mixed state (H-c1 < H < H-c2) and the surface superconductivity state (H-c2 < H < H-c3) around 4 K. The sample was a sputtered him of Nb with a 3 mu m thickness on a 5 mm Si crystal substrate. The measurements were carried out on the CRISP reflectometer at the ISIS facility, with field strengths between 400 and 4500 Oe. We present preliminary data for the spin-dependent reflectivity as a function of applied field. (C) 1998 Elsevier Science B.V. All rights reserved.

Abstract:

In this paper I enumerate the possible magnetic structures that may be observed in RBa2Cu3O6+x compounds when a bilinear coupling exists between the R and Cu magnetic moments. I discuss the implications of this coupling for local relaxation probes at the R site. (C) 1998 Elsevier Science B.V. All rights reserved.

Abstract:

We report a preliminary study of the Pr3+ ground-state multiplet of Pr2NiO4. The crystal field energy levels are determined from neutron scattering and specific heat data, and an analysis is presented in terms of an approximate tetragonal crystal field model, The low-temperature magnetic properties of Pr3+ are governed by two singlets of Gamma(1) and Gamma(2) symmetry, respectively, separated in energy by 4.3 meV. No magnetic ordering of the Pr sublattice has been detected.

Abstract:

We have used inelastic neutron scattering to study the magnetic excitations in CuO, a quasi 1-D antiferromagnet, along the chain direction, [zeta, 0, <(zeta)over bar>]. The low-energy excitations can be described adequately by linear spin wave theory, but at high energies the magnetic scattering exhibits characteristics of the spinon model.