Geometrical magnetic frustration in rare-earth chalcogenide spinels

Abstract

We have characterized the magnetic and structural properties of the $\mathrm{Cd}{\mathit{Ln}}_{2}{\mathrm{Se}}_{4}$ $(\mathit{Ln}=\mathrm{Dy},\mathrm{Ho})$, and $\mathrm{Cd}{\mathit{Ln}}_{2}{\mathrm{S}}_{4}$ $(\mathit{Ln}=\mathrm{Ho},\mathrm{Er},\mathrm{Tm},\mathrm{Yb})$, 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 ${\ensuremath{\Theta}}_{\mathrm{W}}\ensuremath{\sim}\ensuremath{-}10\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, except $\mathrm{Cd}{\mathrm{Yb}}_{2}{\mathrm{S}}_{4}$ for which ${\ensuremath{\Theta}}_{\mathrm{W}}\ensuremath{\sim}\ensuremath{-}40\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The absence of magnetic long-range order or glassiness above $T=1.8\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ 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.