  We report the magnetic properties of the ZnLn2S4 (Ln = Er, Tm, Yb) olivines,
in which the magnetic lanthanide ions are in a potentially frustrated geometry
consisting of sawtooth chains of corner-sharing triangles. Fits to the high
temperature magnetic susceptibility yielded Curie-Weiss temperatures of theta ~
-4, -13, and -75 K for the Er, Tm, and Yb compounds respectively.
Antiferromagnetic interactions indicated by these negative theta values, along
with the absence of magnetic long range order above T = 1.8 K, suggest that
geometrical frustration of magnetic ordering exists in these sulfide olivines
as has been observed previously in the rare earth chalcogenide spinels.
