Stabilisation of the helical phase in epitaxial Y/DyxTb1−x/Y trilayers

DyxTb1−x films (400 Å thick) have been grown between two Y layers by molecular beam epitaxy on sapphire substrates. Their magnetic behaviour has been studied by magnetisation measurements. The occurrence of the helical phase in the Tb epitaxial film is clearly evidenced from the observation of a cusp on the magnetisation versus temperature curve at 228 K. The thermal evolution of the critical fields, for which the alloys undergo the ferromagnetic transition, shows that the helical phase is stabilised down to low temperature for 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 materials.