MAGNETIC-STRUCTURE AND EXCITATIONS OF RARE-EARTH SUPERLATTICES

Rare-earth superlattices have been grown using molecular beam epitaxy and their chemical and magnetic structure determined with X-ray and ne utron diffraction techniques. When the superlattices consist of Ho and the non-magnetic materials Y or Lu, the helical magnetic order in the Ho layers propagates through the non-magnetic blocks with coherence i n both the phase and chirality of the magnetic order. In contrast, whe n superlattices of Ho are grown with other magnetic rare earths, Pr ar id Pr, the coherence between the ordering in the Ho blocks is either r educed or completely absent. It is suggested that the reason for this difference in behaviour is that a helical spin density wave can propag ate in the non-magnetic Y and Lu, but that it is inhibited in the Er b locks by the competing c-axis magnetic ordering and in the Pr blocks b y the different electronic structure and Fermi surface.