Model calculation of thermal conductivity in antiferromagnets

•The Boltzmann equations of phonons and magnons in antiferromagnets have been studied.•Model operators have been used to represent the magnon–phonon and three-phonon interactions.•The models possess the same important properties as the exact operators.•A new expression for the thermal conductivity has been derived.•The results showed a good quantitative agreement with the experimental data of FeCl2.

A theoretical study is given of thermal conductivity in antiferromagnetic materials. The study has the advantage that the three-phonon interactions as well as the magnon phonon interactions have been represented by model operators that preserve the important properties of the exact collision operators. A new expression for thermal conductivity has been derived that involves the same terms obtained in our previous work in addition to two new terms. These two terms represent the conservation and quasi-conservation of wavevector that occur in the three-phonon Normal and Umklapp processes respectively. They gave appreciable contributions to the thermal conductivity and have led to an excellent quantitative agreement with the experimental measurements of the antiferromagnet FeCl2.