Magnetic frustration in the sawtooth lattice of ZnLn2S4 (Ln = Er, Tm,   Yb) olivines
  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. 
G.C. Lau, B.G. Ueland, R.S. Freitas, M. L. Dahlberg, P. Schiffer, and   R.J. Cava