Low temperature specific heat of the Kondo-semimetal CeNiSn in zero and applied magnetic fields

The specific heat of several CeNiSn single crystals of various purity has b een measured in the temperature rang from 25 mK to 5 K and in magnetic fiel ds from zero to 7 Tesla. At very low temperatures (below similar to 200 mK) the specific heat is found to vary linearly wit temperature (C = gamma T), the coefficient gamma decreasing with increasing purity. Above 200 mK, the specific heat is well described as the sum of a linear and a quadratic ter m. An applied magnetic field affects mostly the linear term, which first sl ightly decreases, then strongly increases with field. In magnetic fields, a nuclear hyperfine specific heat contribution is superimposed, which is due mostly to the bare Zeeman-splitting of the Sn-115, Sn-117, Sn-119 nuclei ( all with spin I = 1/2 and with abundances of 0.35, 7.61, and 8.58% respecti vely) in the externally applied field. The results on the specific heat at very low temperatures in applied fields fit into the model of an enhanced ( heavy-fermion type) density of states which is modified by coherent antifer romagnetic fluctuations into a V-shaped density of states at the Fermi ener gy.