The very-low-temperature thermal conductivity ($\kappa$) is studied for BaCo${}_2$V${}_2$O${}_8$, a quasi-one-dimensional Ising-like antiferromagnet exhibiting an unusual magnetic-field-induced order-to-disorder transition. The nearly isotropic transport in the longitudinal field indicates that the magnetic excitations scatter phonons rather than conduct heat. The field dependence of $\kappa$ shows a sudden drop at $\sim 4$ T, where the system undergoes the transition from the Néel order to the incommensurate state. Another dip at lower field of $\sim 3$ T indicates an unknown magnetic transition, which is likely due to the spin-flop transition. Moreover, the $\kappa \left(H\right)$ in the transverse field shows a very deep valleylike feature, which moves slightly to higher field and becomes sharper upon lowering the temperature. This indicates a magnetic transition induced by the transverse field, which however is not predicted by the present theories for this low-dimensional spin system.

• Received 29 December 2011

DOI:https://doi.org/10.1103/PhysRevB.85.134412