Magnetoelasticity in rare-earth superlattices and films

Elastic constraints on rare-earth superlattices and films grown by molecular beam epitaxy strongly perturb their magnetic structure compared to the bulk materials. Continuing studies of Dy/Y and Er/Y superlattices and Dy and Er thin films by neutron scattering and SQUID magnetometry have provided new insight into the interplay of magnetoelastic and exchange interactions in rare earths. The most striking result of the epitaxial clamping to the substrate and intervening non-magnetic layers is the suppression of the ferromagnetic transitions found in bulk Dy and Er. A quantitative calculation of the magnetoelastic energies confirms their importance in driving these phase transitions. The helical and linear spin density wave orderings are also significantly perturbed. For example, in the Dy supperlattices the temperature dependence of the interlayer turn angle is weakened as the elastic clamping is increased. This temperature dependence is completely suppressed in the Er superlattices where the turn angle is typically fixed at the commensurate lock-in value 2π 7 . In the thin films, however, the turn angles are closer to the bulk values. There is also a 50% reduction of the basal plane ordering temperatures compared to bulk Er. For Er the temperature dependence of the exchange is also crucial for explaining these effects.