Depth-dependent magnetism of layered superconductors: Nb/Si

Abstract

We have studied magnetic field penetration and vortex line formation in a [Nb(100 Å)/Si(15 Å)]×20 multilayer by magnetization and polarized neutron reflection. With the magnetic field applied parallel to the surface, the magnetization revealed the presence of a kink above Hcl indicative of transitions between one row of fluxoids and two rows of fluxoids parallel to the surface. The spin dependence of neutron reflectivity below Hcl was consistent with a penetration depth of 1200 Å, substantially larger than that of bulk Nb. In the mixed phase (H ext>Hcl) the field was found to penetrate the surface, with a slope as found in the case of Hext<Hcl. At Hext>Hcl vortices form inside the multilayer, in addition to there being surface penetration. A modulation of the vortex fields was found with the periodicity of the Nb/Si bilayers as evidenced by the spin dependence of the reflectivity at the first Bragg peak of the multilayer. © 1998 American Institute of Physics.