Magnetic properties of orthorhombic fluorite-related oxides Ln3SbO7 (Ln=rare earths)

Ternary rare earth antimonates Ln3SbO7 (Ln=rare earths) were prepared and their structures were determined by X-ray diffraction measurements. They crystallize in an orthorhombic superstructure of cubic fluorite (space group Cmcm for Ln=La, Pr, Nd; C2221 for Ln=Nd–Lu), in which Ln3+ ions occupy two different crystallographic sites (the 8-coordinated and 7-coordinated sites). Their magnetic properties were characterized by magnetic susceptibility and specific heat measurements from 1.8 to 400 K. The Ln3SbO7 (Ln=Nd, Gd–Ho) compounds show an antiferromagnetic transition at 2.2–3.2 K. Sm3SbO7 and Eu3SbO7 show van Vleck paramagnetism. Measurements of the specific heat down to 0.4 K for Gd3SbO7 and the analysis of the magnetic specific heat indicate that the antiferromagnetic ordering of the 8-coordinated Gd ions occur at 2.6 K, and the 7-coordinated Gd ions order at a furthermore low temperature.