Calorimetric Investigation of Hyperfine Interactions in Metallic Praseodymium and Thulium

The nuclear specific heat due to hyperfine interactions has been measured for the rare-earth metals Pr and Tm in the temperature range 0.02-0.4 K. The results for Pr strongly support the suggestion that the electronic magnetic moments are ordered on only half the sites of the double-hcp lattice, and that this order is sinusoidally modulated in space. The maximum value of the electronic moment is $0.95{\mu }_B$ as compared with the free-ion moment of $3.2{\mu }_B$. The maximum hyperfine splittings are +0.0624±0.0008 and -0.0032±0.0002 K for the magnetic dipolar and the electric quadrupolar interactions, respectively. The data for Tm are indicative of a magnetic hyperfine splitting of -0.1072±0.0008 K, which is 5% less than expected for the fully saturated electronic moment.