The specific heats of metallic Ho and Tb have been measured between 0.03 and 0.5°K, a temperature range in which the nuclear (hyperfine) heat capacity predominates. The data are fitted with theoretical Schottky curves, using magnetic dipole hyperfine-interaction parameters $a^{\prime }=+0.319\mathrm{}°$K and $a^{\prime }=+0.149\mathrm{}°$K, and electric quadrupole coupling constants $P=+0.004\mathrm{}°$K and $P=+0.0158\mathrm{}°$K for Ho and Tb, respectively. For Tb, these values are in agreement with the parameters obtained from nuclear-magnetic-resonance measurements. An earlier suggestion by the present authors that a cooperative nuclear-nuclear interaction might be present in Tb is here shown to have been based on an erroneous temperature scale. A detailed description of the calorimeter is presented.

• Received 22 July 1968

DOI:https://doi.org/10.1103/PhysRev.177.910