Anomalous thermal expansion in Er-32/Lu-10 superlattice

We have determined the magnetoelastic (MEL) stresses M-12(alpha) and M-22(a lpha), respectively accounting for the volume and c/a distortions of the HC P structure, for an [Er-32/Lu-10](40) superlattice. The MEL stresses were r espectively determined from the temperature dependencies of the c and a lat tice 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 s train dependencies of the crystal electric field and exchange energy intera ctions. Significant differences have been found between the thermal evoluti on of the MEL strains in the SL and in bulk Erbium. There are two main cont ributions to both MEL stresses: one comes from the Er block volume, where i n turn the epitaxy plays a fundamental role with a second order MEL stress of approximate to 10(3) GPa/unit strain at 0 K; the other one comes from th e Er/Lu blocks interface, which is very large, approximate to 50 GPa at 0 K , and of the opposite sign as for bulk Er. (C) 1999 Elsevier Science B.V. A ll rights reserved.