Thermal Conductivity of Paramagnetic Salts at Low Temperatures

Abstract

We present a simple theory of the effect of impurity-induced changes in atomic force constants and changes in atomic mass on the lifetime of coupled spin-phonon modes in paramagnetic crystals. The result is then employed to study the effect of impurity scattering, boundary scattering, and scattering of the coupled modes by longitudinal fluctuations in spin density on the temperature dependence of the thermal conductivity, and the frequency distribution of the heat flux. The theory can account for the experimental data on MgO doped with ${\mathrm{Cr}}^{2+}$ reported recently by Challis, McConachie, and Williams and offers support for the interpretation of the data presented by these authors.