Technique of polarized neutron reflectometry for direct measurement of depth of magnetic field penetration into Nb and YBa₂Cu₃O₇ superconducting films

A direct measurement of the magnetic field penetration depth λ_L into Nb/Si and YBa₁Cu₃O₇/SrTiO₃ has been performed by polarized neutron reflectometry. Measurements were made at two scattering geometries: reflection from the `vacuum-film' side and from the `substrate-film' side. For the first time the spectral dependence of the spin asymmetry SA = (R⁺-R^-)/(R⁺+R^-), where R⁺ and R^- are the spin-dependent coefficients of the neutron reflection, was measured for a YBa₂Cu₃O₇ film in a wide range of transferred momenta. The values of λ_L = (1400±100) angstroms at T = 4.8 K (H = 500 E) and λ_L = (1350±150) angstroms at T = 2 K (H = 300 E) were measured along the c-axis oriented perpendicular to the film surface for both scattering geometries.