Penetration depth of YBa2Cu3O7 measured by polarised neutron reflectometry

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.