The magnetic structures of the CeScSi-type GdMgSn and GdMgPb compounds have been studied by both neutron powder diffraction and Mössbauer spectroscopy (${}^{119}Sn$ and ${}^{155}Gd$). The neutron diffraction results show that the two compounds adopt incommensurate antiferromagnetic structures at 5.4 K with propagation vectors $\vec{k}=[0.910,0.077,0]$ for GdMgSn and $\vec{k}=[0.892,0,0]$ for GdMgPb. The magnetic moments lie in the basal plane, which is confirmed by both ${}^{119}Sn$ and ${}^{155}Gd$ Mössbauer spectroscopy. Mössbauer 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 $T\sim 40$ 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.

• Received 24 February 2014

DOI:https://doi.org/10.1103/PhysRevB.89.174428