  Heat-capacity (C) and ac susceptibility measurements have been performed on
the spin-chain compounds, Sr3ZnRhO6 and Ca3NiMnO6, to establish their magnetic
behavior and to explore whether there are magnetic frustration effects due to
antiferromagnetic coupling of the chains arranged in a triangular fashion.
While the paramagnetic Curie temperatures have been known to be large with a
negative sign, as though antiferromagnetic interaction is very strong, the
results establish that (i) the former apparently undergoes inhomogeneous
magnetic ordering only around 15 K, however without spin-glass anomalies, and
(ii) the latter orders antiferromagnetically at a relatively low temperature
(17 K). Thus, the magnetic frustration manifests differently in these
compounds.
