Specific Heat of Terbium Metal between 0.37 and 4.2°K

The specific heat Cₚ of terbium metal, measured between 0.37 and 4.2^∘{}K in a He³ cryostat, could be separated by a least squares analysis into three contributions; the lattice specific heat CL=0.58T³ (corresponding to a Debye θ=150^∘K), the electronic specific heat CE=9.05T, and the nuclear specific heat CN=238T^-2-11.9T^-3-4.5T^-4+0.38T^-5+0.06T^-6 (Cₚ in mJ/mole ^∘{}K). CN is due to the splitting of the nuclear spin states by the magnetic field Heff of the $4f$ electrons and by the nuclear electric quadrupole coupling. In the series expansion for CN there are only two independent constants, the magnetic hyperfine constant a^' and the quadrupole coupling constant P. Our experimental values of a^'=0.150^∘K and P=0.021^∘K are in good agreement with results obtained by electron paramagnetic resonance and nuclear magnetic resonance techniques which gave a^'=0.152^∘K and P=0.029^∘K. By assuming μ=1.52 nuclear Bohr magnetons for Tb¹⁵⁹ one obtains Heff=4.1 MG. In sharp contrast with earlier results, our measurements revealed no anomalies in Cₚ between 1 and 4^∘{}K. Such anomalies thus were probably caused by impurities in the samples of the other investigators.