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 TN=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.