Magnetism of a rhombohedral-type pyrochlore-derived Kagome series, Mn2R3Sb3O14 (R= Rare-earths)

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.