Temperature evolution of the umbrella structure in holmium iron garnet

Using neutron diffraction data, the thermal evolution of the magnetic structure of Ho₃Fe₅O₁₂ has been studied. Below the compensation temperature (T_comp=137 K), the umbrella structure parameters which fit the spontaneous ferrite magnetizations have been determined. AboveT_comp, the compound behaves as a Néel type ferrimagnet. Particular attentions have been given to the magnetic form factors of both iron sublattice on one hand and on the other hand to a rhombohedral distorsion fromI a3d toR below 30 K and in first approximation toRc forT>30 K.