Abstract
A simple model for calculating the Ruderman-Kittel-Kasuya-Yosida exchange interaction between layers of a magnetic rare-earth (RE) metal separated by yttrium is presented. The calculation is semiphenomenological and makes use only of previously measured or calculated quantities. It is valid when the thickness of the magnetic RE layers is much smaller than that of the Y layers. The coupling is found to be of fairly long range and to be consistent in sign with the ordering observed in Gd-Y superlattices. For the actual case of comparable layer thicknesses, a discussion of the superlattice wave functions is given. We show that our simple model is very plausible for constituent metals with simple band structures. For the actual band structure of Gd, eigenstates that are evanescent in the Gd region may provide a justification of our model and account for the agreement with experiment. Further theoretical and experimental work is necessary for understanding these systems.