XRD STUDIES OF H-T PHASE-DIAGRAMS OF ER AND HO

We present results of X-ray diffraction on Er and Ho single crystals i n the temperature range 4.2-100 K in magnetic fields up to 50 kOe, wit h the applied field parallel and normal to the [001] axis. Lattice par ametric field-temperature relationships of a(T, H) and c(T, H) indicat e the occurrence of both field effects on spontaneous transitions at T -C(H) and T-N(H) and certain novel field-induced transitions of the fi rst and second order, as caused by the deformation spin structures. H- T phase diagrams for Er and Ho are presented.