Thermal transport of the single-crystal rare-earth nickel borocarbides $R{\mathrm{Ni}}_2{\mathrm{B}}_2\mathrm{C}$

The quaternary intermetallic rare-earth nickel borocarbides $R{\mathrm{Ni}}_2{\mathrm{B}}_2\mathrm{C}$ are a family of compounds that show magnetic behavior, superconducting behavior, and/or both. Thermal transport measurements reveal both electron and phonon scattering mechanisms, and can provide information on the interplay of these two long-range phenomena. In general the thermal conductivity $\kappa$ is dominated by electrons, and the high temperature thermal conductivity is approximately linear in temperature and anomalous. For $R=\mathrm{Tm},$ Ho, and Dy the low-temperature thermal conductivity exhibits a marked loss of scattering at the antiferromagnetic ordering temperature $T_N.$ Magnon heat conduction is suggested for $R=\mathrm{Tm}.$ The $\kappa$ data for $R=\mathrm{Ho}$ lends evidence for gapless superconductivity in this material above $T_N.$ Unlike the case for the non-magnetic superconductors in the family, $R=\mathrm{Y}$ and Lu, a phonon peak in the thermal conductivity below $T_c$ is not observed down to $T=1.4\mathrm{}\mathrm{K}$ for the magnetic superconductors. Single-crystal quality seems to have a strong effect on $\kappa .$ The electron-phonon interaction appears to weaken as one progresses from $R=\mathrm{Lu}$ to $R=\mathrm{Gd}.$ The resistivity data shows the loss of scattering at $T_N$ for $R=\mathrm{Dy},$ Tb, and Gd; and the thermoelectric power for all three of these materials exhibits an enhancement below $T_N.$