  Several doped 6H hexagonal ruthenates, having the general formula Ba3MRu2O9,
have been studied over a significant period of time in order to understand the
unusual magnetism of ruthenium metal. However, among them, the M=Fe compound
appears different since it is observed that unlike others, the 3d Fe ions and
4d Ru ions can easily exchange their crystallographic positions and as a result
many possible magnetic interactions become realizable. The present study
involving several experimental methods on this compound establish that the
magnetic structure of Ba3FeRu2O9 is indeed very different from all other 6H
ruthenates. Local structural study reveals that the possible Fe/Ru-site
disorder further extends to create local chemical inhomogeneity, affecting the
high temperature magnetism of this material. There is a gradual decrease of
57Fe M\"ossbauer spectral intensity with decreasing temperature (below 100 K),
which reveals that there is a large spread in the magnetic ordering
temperatures, corresponding to many spatially inhomogeneous regions. However,
finally at about 25 K, the whole compound is found to take up a global
glass-like magnetic ordering.

Materials Science