STABILIZATION OF THE HELICAL PHASE IN EPITAXIAL Y DYXTB1-X/Y TRILAYERS/

DyxTb1-x films (400 Angstrom thick) have been grown between two Y laye rs by molecular beam epitaxy on sapphire substrates. Their magnetic be haviour has been studied by magnetisation measurements, The occurrence of the helical phase in the Tb epitaxial film is clearly evidenced fr om the observation of a cusp on the magnetisation versus temperature c urve at 228 K. The thermal evolution of the critical fields, for which the alloys undergo the ferromagnetic transition, shows that the helic al phase is stabilised down to low temperature far x = 1 and x = 0.78. Because of epitaxial strains, for all the DyxTb1-x alloys, the Curie temperature is significantly lowered compared to the values in bulk ma terials.