MAGNETOELASTIC AND EXCHANGE CONTRIBUTIONS TO THE HELICAL-FERROMAGNETIC TRANSITION IN DYSPROSIUM EPITAXIAL-FILMS

The Curie temperature of dysprosium films epitaxially grown on yttrium and on erbium is shown to increase continuously with the epitaxial st rain induced along the c-axis. This variation is correlated to modific ations of the alpha strains, of the gamma distortion and of the exchan ge energy barrier. The evolution of these different terms is discussed from the experimental thermal variations of the lattice parameters an d turn angles determined by neutron diffraction.