Geometrical magnetic frustration in rare-earth chalcogenide spinels

We have characterized the magnetic and structural properties of the Cd Ln2 Se4 (Ln=Dy,Ho), and Cd Ln2 S4 (Ln=Ho,Er,Tm,Yb), spinels. We observe all compounds to be normal spinels, possessing a geometrically frustrated sublattice of lanthanide atoms with no observable structural disorder. Fits to the high-temperature magnetic susceptibilities indicate these materials to have effective antiferromagnetic interactions, with Curie-Weiss temperatures ΘW ∼-10 K, except Cd Yb2 S4 for which ΘW ∼-40 K. The absence of magnetic long-range order or glassiness above T=1.8 K strongly suggests that these materials are a different venue in which to study the effects of strong geometrical frustration, potentially as rich in interesting physical phenomena as that of the pyrochlore oxides.