Thermal conductivity and electrical resistivity of gadolinium as functions of pressure and temperature

Abstract

The electrical resistivity ρ and the thermal diffusivity a of gadolinium have been measured as functions of T in the range 45–400 K. The thermal conductivity λ has been calculated from a and experimental data for the specific-heat capacity, $c_p$. λ can be analyzed in terms of simple models for the lattice and electronic components above the Curie temperature $T_C$≃291.4 K. Below $T_C$ an additional term, identified as a magnon (spin-wave) thermal conductivity ${\lambda }_m$, is found. ρ and λ have also been studied as functions of T and P in the range 150–400 K and 0–2.5 GPa. The Lorenz function L=ρλ/T increases by about 20%/GPa under pressure due to a very strong pressure dependence of the lattice thermal conductivity. The pressure coefficients of ρ and λ are -5.1×${10}^{\mathrm{-}2}$ and 0.22 ${\mathrm{GPa}}^{\mathrm{-}1}$, respectively, at 300 K (above $T_C$), and 0 and 0.16 ${\mathrm{GPa}}^{\mathrm{-}1}$ at 200 K (below $T_C$). $T_C$ and the spin-reorganization temperature $T_r$≃219 K both decrease under pressure, at the rates -14.0 and -22.0 K/GPa, respectively. Although the magnitude of ${\lambda }_m$ cannot be accurately calculated from the zero-pressure data for λ, the temperature dependence of dλ/dP allows us to distinguish between several models and assign a value of ${\lambda }_m$≃1.5 W ${\mathrm{m}}^{\mathrm{-}1}$ ${\mathrm{K}}^{\mathrm{-}1}$, or 16.0% of λ, at 200 K.