Thermal conductivity of BaCo2V2O8

BaCo2V2O8 is a quasi one-dimensional antiferromagnetic Ising-like spin-chain. The chain can be described by an effective S=1/2 1D XXZ model with coupling constant J≅65 K and anisotropy parameter ε = 0.46. Parallel to the c axis the magnetization saturates at Hsparallel ≅23 T and perpendicular to the c axis at Hsparallel ≅ 41 T. At zero field, the system orders at TN=5.4 K. The Neel order is suppressed by a magnet field with very different rates depending on the direction of the applied field. We measured the thermal conductivity parallel (κ parallel) and perpendicular (κ perpendicularto) to the chains in the temperature range from room temperature down to 250 mK. For both directions, we observe a sharp anomaly at TN and two maxima, one in the ordered phase and one above. In the ordered phase, the thermal conductivity is isotropic (κ parallel = κ perpendicularto), while above TN, κ parallel is significantly higher than κ perpendicularto. As this may suggest an additional magnetic contribution to κ parallel in the disordered phase, we compare our data to numerical calculations of the anisotropic κ using the 1D XXZ model Hamiltonian. Moreover, we analyze the field dependence of κ for different directions of the applied magnetic field.