Anomalous low-temperature behavior of the Co dimers in the oxo-halide CoSb2O3Br2

✍ Scribed by Zuzana Hugonin; Mats Johnsson; Sven Lidin; Dirk Wulferding; Peter Lemmens; Reinhard K. Kremer

• Publisher: Elsevier Science
• Year: 2008
• Tongue: English
• Weight: 944 KB
• Volume: 181
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1016/j.jssc.2008.07.005

✦ Synopsis

We report the synthesis, crystal structure determination, magnetic and low-temperature structural properties of a new cobalt antimony oxo-bromide. CoSb 2 O 3 Br 2 crystallizes in the triclinic crystal system, space group PÀ1, with the following lattice parameters:

32(4)1, and Z ¼ 2. The crystal structure was solved from single crystal X-ray data and refined on F 2 , R 1 ¼ 3.08. The structure consists of layers made up by three building blocks, [CoO 4 Br 2 ], [SbO 3 Br], and [SbO 3 ] that are connected via edge-and corner-sharing so that structural Co-Co dimers are formed. The layers have no net charge and are only weakly connected by van der Waals forces to adjacent layers. Above $25 K the magnetic susceptibility is independent of the magnetic field and can be very well described by a Curie-Weiss law. Below 25 K the susceptibility passes through a maximum and decreases again that is typical for the onset of long-range antiferromagnetic correlations. Long-range antiferromagnetic ordering is observed below T N $9 K indicating substantial inter-dimer exchange coupling between Co-Co dimers within the layers. However, according to the heat capacity results only a minute fraction of the entropy is associated with the long-range ordering transition. The phonon anomalies observed for To6 K in Raman scattering and an anomaly in the specific heat point to a structural instability leading to a loss of inversion symmetry at lowest temperatures.