Neutron reflectometry studies of Gd/Nb and Cu₃₀Ni₇₀/Nb superlattices

We performed a comparative study of magnetic proximity effects in [Gd(5nm)/Nb(25nm)]₁₂ and [Cu₃₀Ni₇₀(6nm)/Nb(27nm)]₁₂ superlattices of S/F type by means of transport measurements and neutron scattering. Transport measurements have shown that Gd/Nb and CuNi/Nb superlattices shows 3D and 2D type of superconductivity respectively. In the case of proximity coupled Gd/Nb superconductor the effective thickness of the superconducting region, 300nm is enough to expel significant amount of applied magnetic field which was detected by neutron scattering. In decoupled CuNi/Nb superlattice thickness of every superconducting layer is only 27nm which is not enough to expel applied magnetic field. Our study shows how neutron reflectometry can be applied to study proximity coupling in superconducting/ferromagnet heterostructures. (paper)