Anomalous thermal expansion in Er 32/Lu 10 superlattice

Abstract

We have determined the magnetoelastic (MEL) stresses M α 12 and M α 22, respectively accounting for the volume and c/a distortions of the HCP structure, for an [Er 32/Lu 10] 40 superlattice. The MEL stresses were respectively determined from the temperature dependencies of the c and a lattice parameters, as obtained from X-ray diffraction experiments. A model is used in order to determine the MEL stresses, which are the result of the strain dependencies of the crystal electric field and exchange energy interactions. Significant differences have been found between the thermal evolution of the MEL strains in the SL and in bulk Erbium. There are two main contributions to both MEL stresses: one comes from the Er block volume, where in turn the epitaxy plays a fundamental role with a second order MEL stress of ≈10 3 GPa/unit strain at 0 K; the other one comes from the Er/Lu blocks interface, which is very large, ≈50 GPa at 0 K, and of the opposite sign as for bulk Er.