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Zusammenfassung:
The polycrystalline sample of a new osmate Ba3Os2O9 was synthesized by solid-state reactions. It crystallizes in Cs3Tl2Cl9-type structure, R (3) over bar cH (No. 167), and is electrically semiconducting with activated conduction behavior. No clear evidence for magnetic ordering is observed in the magnetic susceptibility. Instead it displays a very broad maximum around 170 K, indicating the onset of antiferromagnetic correlations, likely connected with the formation of magnetic dimers with an intra-dimer exchange, J congruent to 175 K. However, an analysis of the susceptibility reveals a reduced, but still finite susceptibility at low-temperature, in contrast to the fully gapped behavior expected for a simple dimer system. This suggests the presence of additional inter-dimer interactions, which might be frustrated and thus prevent a stable antiferromagnetic ordered state. The effective moment of 1.59 mu(B)/Os deduced from a dimer fit is much lower than the expected spin-only value of 2.83 mu(B), in accordance with expected strong spin-orbit interaction.
