Magnetic transitions and magnetoelasticity in double rare earth superlattices

We report on zero field cool susceptibility (chi (ZFC)), magnetization (M) and magnetoelastic stress (MELS) measurements, in the range 8-200 K and up to 12 T applied magnetic field, on (0001) superlattices [Ho-15/Dy-30](50) a nd [Ho-30/Dy-15](50). Magnetic phase diagrams are proposed, with a wide var iety of magnetic phases: paramagnetic, helical, helifan, fan and ferromagne tic. Same magnetic phases for Dy and Ho coexist. Exchange polarization of H o layers by Dy ones is manifested. Although compressed by basal plane a-lat tice parameter misfit, spontaneous ferromagnetic order in Dy layers is supp ressed, as well as ferro-cone phase in stretched Ho ones. However, modest a pplied magnetic field along b-axis (H congruent to 0.6 T, at 10 K) produces ferromagnetic order in Dy (in basal plane) and ferro-cone in Ho. The basal plane hexagonal symmetry breaking magnetoelastic stress M-gamma ,M-2 (T = 0, 12 T) is separated for Ho and Dy layers, in good agreement with single-i on magnetoelastic coupling model. (C) 2001 Elsevier Science BY. All lights reserved.