STABILIZATION OF THE HELICAL PHASE IN TB AND IN DYXTB1-X ALLOYS FILMSGROWN EPITAXIALLY ON Y

Neutron diffraction experiments and macroscopic magnetization measurem ents show evidence of the stabilization of the helical magnetic phase over large temperature ranges for Tb and DyxTb1-x alloy films grown ep itaxially on yttrium. In particular, the temperature of the transition between the helical and the ferromagnetic states is shifted from 220 K for bulk terbium to 160 K for a pure terbium film grown epitaxially on yttrium, despite the low stability of the helical phase in the bulk element. The decrease of the Curie temperature is due to the negative c-axis strain induced by the epitaxial growth on yttrium. The epitaxi al strains also induce modifications of the Fermi surface, which leads to an increase of the turn angle even at T-N. At low temperature, a l ong-wavelength-modulated phase, whose origin still remains to be expla ined, has been observed.