Transport Properties of Thulium Single Crystals

Single crystals of thulium have been grown by the strain-anneal technique. The electrical resistivity, thermal conductivity, and Seebeck coefficients were measured along the 〈112̄0〉 (a-axis), 〈101̄0〉 (b-axis), and $〈0001〉$ (c-axis) crystallographic directions as a function of temperature from 5 to 300^∘{}K. All measurements indicated a magnetic transition near 57^∘{}K, in good agreement with a N\'eel temperature of 56^∘{}K as determined in earlier work by the Oak Ridge National Laboratory neutron diffraction group. The Seebeck coefficient measured along the c axis exhibited a second anomaly at 32^∘{}K, in agreement with low-field ac susceptibility measurements; but this anomaly did not appear in the neutron-diffraction measurements. The anomalies observed in the electrical resistivity and thermal conductivity at the N\'eel temperature are interpreted in terms of magnetic superzone planes. All transport properties exhibited a significant anisotropy between the a- or b-axis and c-axis directions. The high-temperature anisotropy of the electrical resistivity and the thermal conductivity is interpreted in terms of the anisotropy of the Fermi surface.