Hyperfine heat capacity of metallic europium and erbium

The specific heats of the Rare Earth metals Eu and Er have been measured in the temperature range 0.03 to 0.8K. The measurements yield magnetic hyperfine parameters of 13.2 mK, 5.85 mK, and 42.3 mK for ¹⁵¹Eu, ¹⁵³Eu, and ¹⁶⁷Er, respectively, corresponding to magnetic hyperfine fields of 0.26 and 7.2 MOe for Eu and Er. The nuclear quadrupole coupling constants were found to be ?0.06 mK, ?0.16 mK, and ?2.7 mK for ¹⁵¹Eu, ¹⁵³Eu and ¹⁶⁷Er.