THERMAL CONDUCTIVITIES AND LORENZ FUNCTIONS OF GADOLINIUM TERBIUM AND HOLMIUM SINGLE CRYSTALS

The thermal conductivities of gadolinium, terbium, and holmium single crystals have been measured as a function of temperature from 5 to 300°K. The steady-state heat-flow method was used. For each element measurements were taken in the 112̄0 (a-axis) and in the 0001 (c-axis) directions of the hexagonal close-packed crystal structure. Electrical resistivity measurements were made on the same samples to obtain Lorenz functions. Anomalies near magnetic transition temperatures are interpreted in terms of magnetic superzones and spin-disorder scattering. High-temperature anisotropy is interpreted in terms of Fermi-surface anisotropy. Lorenz numbers appreciably larger than L0 suggest that phonons and magnons, in addition to electrons, can carry heat. © 1969 The American Physical Society.