The thermal conductivity of the two-dimensional magnetic systems ${\left({\mathrm{C}}_n{\mathrm{H}}_{2n+1}\mathrm{N}{\mathrm{H}}_3\right)}_2\mathrm{Cu}{\mathrm{Cl}}_4$ (with $n=1,2\mathrm{}$) has been measured from $0.12T_c$ to $2.5T_c$ in fields up to 6.5 T. We found a considerable heat transport by the magnetic system, both below and above $T_c$. Above $T_c$ this heat transport can be attributed to magnonlike states which can exist well into the paramagnetic region in low-dimensionality systems.

• Received 2 May 1977

DOI:https://doi.org/10.1103/PhysRevLett.39.467