The layered honeycomb material ${\mathrm{BaCo}}_2{\left({\mathrm{AsO}}_4\right)}_2$ is of topical interest because its magnetic state is related to that of the Kitaev magnet $\alpha \text{−}{\mathrm{RuCl}}_3$. Using thermal transport to probe how magnetic excitations interact with phonons in the magnetically disordered regime, we have uncovered an unusually large enhancement of the thermal conductivity ${\kappa }_{xx}$ in an in-plane magnetic field $\mathbf{H}$. Just above the Néel temperature $T_{\mathrm{N}}$, a field of 13 T increases ${\kappa }_{xx}$ by a factor of $\sim 211$, which is very large compared to other magnetic insulators. Interestingly, ${\kappa }_{xx}(H,T)$ exhibits a scaling behavior in the entire magnetically disordered region that surrounds the ordered zigzag state. The ratio $\mathrm{\Delta }{\kappa }_{xx}(H,T)/{\kappa }_{xx}(13,T)$, measured throughout the disordered region, collapses to a one-parameter scaling function $\exp (-1/gx)$ (where $x={\mu }_{\mathrm{B}}B/k_{\mathrm{B}}T$ and $g$ is a constant).

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• Frustrated magnetism
• Lattice thermal conductivity
• Phonons
• Spin-phonon coupling
• Thermal conductivity