Specific Heat of Holmium Metal between 0.38 and 4.2°K

Between 0.38 and 4.2°K, the specific heat of holmium metal can be expressed $C_p=2.26\mathrm{}{T}^3+10T+C_N$ (in mJ/mole °K). For calculating the nuclear specific heat $C_N$ a Schottky curve for eight energy levels at $\frac{W_i}{k}=a^{\prime }i+P[i^2-\frac{1}{3}I(I+1\mathrm{}\left)\right]$, where $i=-\frac{7}{2}, \cdots , \frac{7}{2}$, must be used. The magnetic hyperfine constant $a^{\prime }=0.320\mathrm{}°$K and the quadrupole coupling constant $P=0.007\mathrm{}°$K. The results below 1°K indicate that a quadrupole term is necessary for representing the data with a Schottky curve. At 0.29°K, where the maximum is reached, $C_N=7000\mathrm{}$ mJ/mole °K and even at 4°K $C_N=269\mathrm{}$ mJ/mole °K, being thus larger than the other contributions to $C_p$ combined. The effective magnetic field at the holmium nuclei is 9.3 MG. Owing to the very large hyperfine interaction the coefficient of the electronic specific heat was obtained from measurements on other rare earths. The $T^3$ term is the sum of lattice and magnetic specific heats and it was calculated from the present results above 2°K. The magnetic heat capacity apparently depends on the thermal history of the metal or on impurities.