Spin-wave dynamics of magnetic heterostructures: application to Dy/Y multilayers.

We examine the spin-wave (SW) dynamics of Dy/Y multilayers in order to separate the contribution of the Dy-Y interface from that of bulk Dy. The SW frequencies and intensities of bulk Dy are determined analytically. When the Dy layers in a multilayer geometry are decoupled, the SW dispersion relations are discontinuous with discrete excitations. With a Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction coupling through the Y spacer, the discrete excitations become dispersive and the main SW branches split due to the multilayer geometry. Regardless of the strength of the intermediate RKKY interaction, the dispersion signature of the bulk remains.