Glasslike ordering and spatial inhomogeneity of magnetic structure in Ba_3FeRu_2O_9:Role of Fe/Ru site disorder

摘要

Several doped 6H hexagonal ruthenates, having the general formula Ba_3FeRu_2O_9 have been studied over a significant period of time 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 Ad 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 establishes that the magnetic structure of Ba_3FeRu_2O_9 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 Mossbauer 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 glasslike magnetic ordering.