Abstract
The long-range helimagnetic order in synthetic rare-earth Dy-Y superlattices has been studied. The magnetic spiral of Dy maintains its coherence in a (Dy 38 Å -Y 38.6 Å ) 80 superlattice, but not in a (Dy 38Å - Y 120.4 Å ) 80 superlattice where the intervening Y layers are 42 atomic planes thick. Furthermore, the spiral periodicity shows a markedly different temperature dependence from that of bulk Dy, including a smaller range of variation and a "lock-in" at low temperature.