Magnetic phase diagram of holmium/dysprosium superlattices

Abstract

We report on the magnetisation measurements with a magnetic field applied along the HCP-structure b-axis for Ho/Dy magnetic superlattices (SLs). The zero-field-cool susceptibility, χ ZFC, shows the magnetic-order coexistence of the Ho and Dy layers, below their respective ordering temperatures. The magnetic-phase diagrams (MPD) of Ho/Dy SLs have been obtained from magnetisation measurements, and we found that the magnetic phases of the Ho and Dy layers are very similar to the bulk ones. Although the analysis of the high-field magnetisation indicates that Ho and Dy do not interact magnetically, this coupling exists at low field. The increment of the Néel temperature in the Ho layers with respect to the bulk could reflect some kind of polarisation between Ho and Dy layers. In the MPD that we have proposed for Ho/Dy SLs, a huge region exists where an helifan phase remains stable for both rare-earth layers, especially for the Ho 30/Dy 15 SL. This could represent the first time that the helifan phase of Ho layers stabilises a similar phase for Dy layers, due to the coherent propagation of conduction band electrons through Ho and Dy layers. However, at low temperatures, we do not expect to find the ferro-cone phase in Ho layers as in the bulk, because of the epitaxial strain in between the Ho and Dy layers of the superlattice.