  Peculiarities of the formation of a neutron enhanced standing wave in the
structure with a thin highly absorbing layer of gadolinium are considered in
the article. An analogue of the poisoning effect well known in reactor physics
was found. The effect is stronger for the Nb/Gd/Nb system. Despite of this
effect, for a Nb/Gd bilayer and a Nb/Gd/Nb trilayer placed between Al2O3
substrate and Cu layer, it is shown theoretically and experimentally that one
order of magnitude enhancement of neutron density is possible in the vicinity
of the Gd layer. This enhancement makes it possible to study domain formation
in the Gd layer under transition of the Nb layer(s) into the superconducting
state (cryptoferromagnetic phase).
