Polarised neutron reflectometry studies of flux penetration in superconducting Nb

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.