Ba2 CoO4: Crystal growth, structure refinement, and physical properties

Single-crystalline Ba2 CoO4 was grown using the floating-zone technique. Single-crystal refinement of x-ray diffraction data indicates that Ba2 CoO4 has a monoclinic structure with a=5.9176(13) Å, b=7.6192(16) Å, c=10.3790(22) Å, and β=91.734(4)° at room temperature. Magnetic susceptibility, specific heat, and thermal conductivity show anomalies at TN =25 K, due to antiferromagnetic ordering. However, the magnitude of the Néel temperature TN is significantly lower than the Curie-Weiss temperature (|θ|≈110 K), suggesting either reduced-dimensional magnetic interactions and/or the existence of magnetic frustration. The latter may be induced by disorder evident from the variable-range-hopping behavior in the electrical resistivity, nonzero T term in the specific heat, and T2 dependence in the thermal conductivity at low temperatures.