Structural and magnetic properties of Er thin films and Er/Y superlattices: Magnetoelastic effects

Abstract

Crystalline erbium thin films and Er/Y superlattices with varying Er-layer thicknesses have been grown by molecular-beam epitaxy. The magnetic and structural properties of these samples have been analyzed by x-ray-scattering, bulk-magnetization, and neutron-diffraction techniques. From a comparison of the data for the two systems, the importance of interfacial strain relative to artificial modulation in shaping the magnetic behavior has been determined. Though the basic nature of the erbium magnetic order is not qualitatively altered in either the thin films or superlattices, the conical ferromagnetic phase is suppressed in all of the samples considered. The enhanced critical fields exhibit a systematic dependence on Er-layer thickness. These effects appear to follow directly from the epitaxial basal-plane strain which is measurable in films over 14 000 \AA{} thick. This strain, along with a ``clamping'' of the Er thermal expansion to the Y lattice, leads to a reduction of the magnitude of the magnetoelastic energy that drives the ferromagnetic transition. The dependence of the magnetoelastic energy on the epitaxial strain is described by a model which accounts for the elastic coupling of the erbium lattice to the yttrium.