Magnetic excitations in Gd/Y and Dy/Y superlattices investigated with inelastic neutron scattering

Investigations of spin waves in magnetic superlattices are of great interest to understand fundamental properties of magnetism in confined structures. Inelastic neutron scattering is the most versatile technique to study magnetic excitations. The theory predicts discrete energy levels and Brillouin zone folding effects for spin waves propagating along the surface normal in rare earth superlattices. To compare with these calculations, we have investigated a number of Gd/Y and Dy/Y superlattices. Here we present inelastic neutron scattering measurements of low energy excitations. Clear dispersive modes from magnetic excitations and indications on discrete energy levels have been found in both superlattice compounds. The modes have a marked field dependence, particularly for the Gd/Y samples in which a spin wave gap is observed in moderate fields. The observations are in broad agreement with the theory