Low-temperature specific heat of uranium monopnictides and monochalcogenides

We present a systematic investigation of the low-temperature specific heat of single-crystalline NaCl-type UX compounds (X=N, P, As, Sb, S, Se, Te) at temperatures between 0.12 and 12 K. It is primarily intended to determine the low-temperature electronic specific heats Cₑ={γ}T of these materials. From our experiments, {γ} increases from UN (25.8 mJ/mole K²) to UAs by a factor of about 2, but is an order of magnitude smaller in USb. For the chalcogenides, a decreasing electronic specific heat with increasing anion size is observed. The measurements at the lowest temperatures reveal the onset of a nuclear Schottky anomaly, from which we derive magnetic hyperfine fields and obtain good agreement with published values from M\"ossbauer experiments for UP and USb. Except for USb, the nuclear heat capacity is negligible at temperatures above 1.5 K.