Magnetic ordering of rare earth monochalcogenides. I. Neutron diffraction investigation of CeS, NdS, NdSe, NdTe and TbSe

The magnetic structures and ordered moments have been determined at 4.2K for the metallic antiferromagnets CeS, NdS, NdSe, NdTe, and TbSe with NaCl structure by means of neutron diffraction. In contrast to the monopnictides, the monochalcogenides of both light and heavy rare earths have FCC type II antiferromagnetic ordering at low temperatures similar to FeO and MnO. Except NdS, where the magnetic moments are tilted by 24 degrees out of the (111) direction, the moments point along the inversion triad which leads to rhombohedral symmetry of the magnetic structure (Shubnikov group R 1 3c). As a consequence of magnetoelastic interactions the FCC lattice of TbSe is rhombohedrally distorted at 4.2K.