Magnetic ordering in strain-controlled epitaxial rare-earth films (abstract)

Abstract

The magnetic properties of epitaxial rare-earth films and multilayers are known to be sensitive to lattice strain arising from the misfit between the substrate and the epitaxial rare earth overlayer. We find that rare-earth films grow epitaxially, with no coherency strain, onto rare-earth fluoride films on GaAs(111) substrates. This decoupling of the rare-earth film from substrate-imposed coherency strain permits controlled amounts of strain to be introduced into the rare earths by suitably designed sandwich structures. We report quantitative x-ray measurements of strain in films of Dy, Ho, and Er sandwiched by rare-earth fluorides and in Er/Dy/Er sandwich structures grown onto rare-earth fluoride buffer films on GaAs(111). SQUID magnetometry of these structures shows that the unstrained Dy, Ho, and Er films exhibit similar Curie temperatures to bulk crystals. On the other hand, in the case of Er/Dy/Er structures the Curie temperature of Dy is increased as a result of a designed, coherency-induced c-axis expansion of the Dy. The results of a study of strain in Y/Dy/Y structures will also be reported.