  The results of magnetic investigations on a new series of compounds,
Mn2R3Sb3O14, containing 2-dimensional Kagome lattice of R ions and belonging to
pyrochlore series, are presented. Crystallographic features of light R members
(R= La, Pr and Nd) of this family, as established in the recent literature,
have been reported to be novel in many respects, in particular, the rhomohedral
nature of the structure which is rare among pyrochlores. It was also reported
that, as the R becomes heavier, beyond R= Sm, the fraction of well-known cubic
pyrochlore phase tends to gradually dominate. Here, we report that we are able
to form the Gd member in the rhombohedral form without noticeable admixture
from the cubic phase. With respect to magnetic behavior, our magnetization
measurements on the La member reveal that Mn exists in divalent state without
any evidence for long range magnetic ordering down to 2 K (that is, suppressed
magnetism), which is not so common for Mn based oxides, though
antiferromagnerism below 2 K is not ruled out. Nd and Gd members, are however,
found to show distinct features above 2 K in magnetic susceptibility and
heat-capacity, attributable to long-range magnetic ordering from respective
rare-earth sublattice. The experimental results with respect to magnetism are
found to be consistent with the results from ab initio band structure
calculations performed for the La case. The calculations imply that electron
correlation is important to describe insulating behavior.
