Low Temperature Specific Heat of the Kondo-Semimetal CeNiSn in Zero and Applied Magnetic Fields

Abstract

The specific heat of several CeNiSn single crystals of various purity has been measured in the temperature range from 25 mK to 5 K and in magnetic fields from zero to 7 Tesla. At very low temperatures (below ∼200 mK) the specific heat is found to vary linearly with temperature (C=γT), the coefficient γ decreasing with increasing purity. Above 200 mK, the specific heat is well described as the sum of a linear and a quadratic term. An applied magnetic field affects mostly the linear term, which first slightly 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 ¹¹⁵ Sn, ¹¹⁷ Sn, ¹¹⁹ Sn nuclei (all with spin I=1/2 and with abundances of 0.35, 7.61, and 8.58% respectively) 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 antiferromagnetic fluctuations into a V-shaped density of states at the Fermi energy.