BaSn6Co6O19—A novel frustrated antiferromagnet with the magnetoplumbite type structure

Single crystals of the novel compound BaSn₆Co₆O₁₉ with maximum width 1 mm and thickness around 0.05 mm were grown from a barium chloride flux. The composition was determined from refinements of single crystal X-ray diffraction data and microprobe analysis. BaSn₆Co₆O₁₉ crystallizes in the magnetoplumbite type structure (hexagonal, space group P6₃/mmc, a=6.0940(1) Å, c=23.9633(5) Å, V=770.69 Å³, Z=2). A significant disorder is generated by random occupation of two octahedrally coordinated crystallographic sites with Co²⁺ and Sn⁴⁺ ions, while further sites are exclusively occupied by either Co²⁺ (tetrahedrally coordinated) or Sn⁴⁺ (octahedrally coordinated). One site with mixed occupation realizes the topology of a kagome net. The temperature dependence of the magnetic susceptibility for a single crystal BaSn₆Co₆O₁₉ reveals a low temperature antiferromagnetic order at T_N=14 K. A relatively large value of frustration factor f_//=|Θ_W//|/T_N≈26 and f_⊥=|Θ_W⊥|/T_N≈12 implies a frustrated antiferromagnetism.