Experimental and theoretical investigations have been made of the spin-wave thermal conductivity of the ferromagnet europium sulfide. Measurements of the thermal conductivity from 1.5-4°K have been made on compressed powders. The theoretical temperature dependence of the spin-wave thermal conductivity below 4°K has been calculated for several external magnetic fields, assuming boundary scattering and considering first- and second-neighbor interactions. With no external magnetic field, the experimental conductivity can be approximately represented by $\mathcal{K}=1.2\mathrm{}{T}^2$ mW/cm(°K) which is reasonably close to the theoretical temperature dependence. However, an external field of 9 kG produced a drop in conductivity ranging from 2 or 3% at 4°K to 25% at 1.5°K; according to theory the conductivity should decrease by 11% at 4°K and 31% at 1.5°K. This disagreement between experiment and theory is quite marked at higher temperatures and will require further study for its resolution.

• Received 7 May 1964

DOI:https://doi.org/10.1103/PhysRev.136.A426