Glass-like ordering and spatial inhomogeneity of magnetic structure in   Ba3FeRu2O9 : The role of Fe/Ru-site disorder
  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. 
Srimanta Middey, Sugata Ray, K. Mukherjee, P. L. Paulose, E. V.   Sampathkumaran, C. Meneghini, S. D. Kaushik, V. Siruguri, ...
cond-mat.mtrl-sci