Effect of high magnetic fields on the heat capacity of single-crystal terbium

The low-temperature (1.3 to 20.0 K) heat capacity of an electrotransport-purified terbium single crystal was measured in magnetic fields up to 10 T applied along the magnetically hard basal-plane direction, i.e., 〈112¯0〉 or a axis. The electronic specific-heat constant, γ=3.71±0.09 mJ/g-at. ${\mathrm{K}}^2$, and the Debye temperature at 0 K, ${\Theta }_D$=169.6±0.8 K, were obtained from an analysis of the zero-field data. The heat capacity is almost independent of the magnetic field below 12 K, but above 12 K systematically increases as a function of increasing field up to ∼3 T and then it remains almost unchanged. This indicates that the spin-wave energy gap due to the magnetic anisotropy in terbium increases with increasing fields at the rate of about 4 and 0.3 K/T below and above ∼3 T, respectively.