Helimagnetic structures in epitaxial Nd/Y superlattices and alloys

The complex magnetic structure of Nd exhibits a new magnetic phase when grown epitaxially, either as a stabilized double hexagonal close-packed alloy, or as part of a Nd/Y superlattice. In the alloy and in those superlattices with small Nd/Y ratios, the incommensurate b axis modulated structure exhibited by elemental Nd at T-N = 19.9 K is absent. In its place, incommensurate helimagnetic order, similar to that in dilute yttrium alloys of the heavy lanthanides, appears below approximately 30 K. Evidence for coherent propagation of the magnetic spiral through the Y spacers is observed in some Y-rich superlattices. As the Nd:Y ratio in the superlattices is increased, the b axis modulated phases reappear and coexist with the helical phase. Thick epitaxial Nd films, nevertheless, exhibit only bulklike magnetic structure. We discuss these observations in terms of band structure modifications.