Calorimetric Investigation of Hyperfine Interactions in Metallic Ho and Tb

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^'=+0.319^∘K and a^'=+0.149^∘K, and electric quadrupole coupling constants P=+0.004^∘K and P=+0.0158^∘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.