Thermal Conductivity and Magnon-Phonon Resonant Interaction in Antiferromagnetic FeCl2

Abstract

The thermal conductivities ${K}_{\ensuremath{\perp}}$ and ${K}_{\ensuremath{\parallel}}$ in the $c$ plane and along the $c$ axis, respectively, have been measured in Fe${\mathrm{Cl}}_{2}$ between 1.2 and 80 \ifmmode^\circ\else\textdegree\fi{}K. Both ${K}_{\ensuremath{\perp}}$ and ${K}_{\ensuremath{\parallel}}$ are found to exhibit, in a wide temperature range, an unusual behavior which reveals the presence of a strong spin-phonon coupling. The experimental results in the antiferromagnetic phase are interpreted on the basis of the magnon-phonon resonant interaction arising from single-ion magnetostriction. It is shown that the thermal conductivity of the resulting magnetoelastic modes can reasonably account for the experimental results: In particular, the anomalous behaviors of ${K}_{\ensuremath{\perp}}$ and ${K}_{\ensuremath{\parallel}}$ between 5 and 17 \ifmmode^\circ\else\textdegree\fi{}K are explained by the effect of a large magnon scattering on the mixed modes. This large scattering leads to a negligible contribution of the spin waves to heat transport. From the ${K}_{\ensuremath{\perp}}$ results, the magnetoelastic coupling constant ${G}_{44}$ is found to be 3.5 meV.