Thermal Conductivity of CaF2, MnF2, CoF2, and ZnF2Crystals

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\ifmmode^\circ\else\textdegree\fi{}K to 300\ifmmode^\circ\else\textdegree\fi{}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 N\'eel temperatures of 67\ifmmode^\circ\else\textdegree\fi{}K and 38\ifmmode^\circ\else\textdegree\fi{}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.