Magnetic phase diagram of holmium/dysprosium superlattices

We report on the magnetisation measurements with a magnetic field applied a long the HCP-structure b-axis for Ho/Dy magnetic superlattices (SLs). The z ero-field-cool susceptibility, chi (ZFC), shows the magnetic-order coexiste nce of the Ho and Dy layers, below their respective ordering temperatures. The magnetic-phase diagrams (MPD) of Ho/Dy SLs have been obtained from magn etisation 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 magnetica lly, this coupling exists at low field. The increment of the Neel temperatu re in the Ho layers with respect to the bulk could reflect some kind of pol arisation 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 bot h rare-earth layers, especially for the Ho-30/Dy-15 SL. This could represen t the first time that the helifan phase of Ho layers stabilises a similar p hase for Dy layers, due to the coherent propagation of conduction band elec trons through Ho and Dy layers. However, at low temperatures, we do not exp ect to find the ferro-cone phase in Ho layers as in the bulk, because of th e epitaxial strain in between the Ho and Dy layers of the superlattice. (C) 2001 Elsevier Science B.V. All rights reserved.