Andrew Boothroyd

Abstract:

We have applied the technique of polarised neutron reflectometry (PNR) to investigate the magnetic held profile near the surface of YBa2Cu3O7 films at 4.3 K. The samples comprised 700-1400 nm of c-axis oriented, single crystal YBa2Cu3O7 deposited by laser ablation on SrTiO3 substrates. The measurements were carried out on the CRISP reflectometer at the ISIS facility.The PNR technique measures the magnetic induction profile perpendicular to the surface, and so in our case the decay of flux in the c-direction was measured with a held applied parallel to the ab plane. We present preliminary data for the polarised and unpolarised reflectivity (C) 1998 Elsevier Science B.V. All rights reserved.

Abstract:

We have used polarised neutron diffraction to measure the magnetisation density induced by an applied magnetic field in single-crystal PrBa2Cu3O6.24. A modified maximum entropy method was employed to invert the diffraction data. The images thus produced show evidence of Pr on the Be site, distortions of the Pr ion, and other interesting features. (C) 1998 Elsevier Science B.V. All rights reserved.

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.