Thermal Conductivity of CaF2, MnF2, CoF2, and ZnF2 Crystals

Abstract

The thermal conductivity of single crystals of Ca${\mathrm{F}}_2$, Mn${\mathrm{F}}_2$, Co${\mathrm{F}}_2$, and Zn${\mathrm{F}}_2$ has been measured over the temperature range from 3°K to 300°K. In this series, Ca${\mathrm{F}}_2$ and Zn${\mathrm{F}}_2$ are diamagnetic, whereas Mn${\mathrm{F}}_2$ and Co${\mathrm{F}}_2$ are antiferromagnetic. All four crystals have nearly equal thermal conductivities at room temperature, but differ at lower temperatures. Ca${\mathrm{F}}_2$, which is nearly isotopically pure, exhibits an exponential rise in conductivity with decreasing temperature characteristic of umklapp processes. Zn${\mathrm{F}}_2$ shows only traces of such umklapp behavior because its conductivity is limited by isotope and impurity scattering. Small cusps are observed in the conductivities of Mn${\mathrm{F}}_2$ and Co${\mathrm{F}}_2$ at their Néel temperatures of 67°K and 38°K, respectively, which indicate the presence of phonon-magnon scattering. Some experimental details concerning thermal conductivity measurements and the behavior of gold-cobalt thermocouples are also given.