Effects of epitaxial strain in Er/Lu thin films

A series of c-axis Er films ranging in thickness from 400 to 9500 A were grown on lutetium base layers to investigate the effects of epitaxial growth on the magnetic properties of bulk erbium. Neutron diffraction studies show that the basal plane lattice parameter of Er approaches the smaller Lu value as the films are made thinner. Below TN the phase angles of the Er spin modulation are diminished from bulk Er values in the thinner films. For all but two 800-A films, there is evidence from bulk magnetization and neutron data of a first-order transition to a conical ferromagnetic state, similar to bulk Er. These phenomena are compared to the properties of Er films grown on yttrium, whose basal plane spacing exceeds that of Er. In these systems the turn angles are greater than bulk and the ferromagnetic phase is suppressed. This contrasting behavior is consistent with predictions from a magnetoelastic energy model of epitaxial constraint developed to describe the Er/Y systems