Neutron powder diffraction and Mössbauer spectroscopy (119Sn and 155Gd) studies of the CeScSi-type GdMgSn and GdMgPb compounds

The magnetic structures of the CeScSi-type GdMgSn and GdMgPb compounds have been studied by both neutron powder diffraction and Mossbauer spectroscopy (119Sn and 155Gd). The neutron diffraction results show that the two compounds adopt incommensurate antiferromagnetic structures at 5.4 K with propagation vectors k =[0.910,0.077,0] for GdMgSn and k =[0.892,0,0] for GdMgPb. The magnetic moments lie in the basal plane, which is confirmed by both 119Sn and 155Gd Mossbauer spectroscopy. Mossbauer spectroscopy refinements and simulations reveal that the magnetic structure of GdMgSn is cycloidal at low temperature and undergoes a transition to a modulated magnetic structure above T∼40 K. A similar magnetic transition is inferred for GdMgPb. The magnetic structures of GdMgSn and GdMgPb are compared with those of other CeScSi-type compounds.