NMR investigations on single crystals of U2Ru2Sn: A Kondo insulator

U2Ru2Sn is unique among all Kondo insulators because of its tetragonal structure and an energy gap of about 150 K being the smallest of all the uranium-based Kondo insulators. We report Knight shift K(T) and relaxation rate T-1(-1) measurements from Sn-119(I = 1/2)-NMR for the first time in single crystals and oriented micro-crystallites. At low temperatures the anisotropy in K(T) increases (K-parallel to /K-perpendicular to(4.2 K) approximate to 2), a trend observed also in chi(T) and rho(T). K(H perpendicular to c) exhibits a smooth variation, whereas for K(H parallel to c) a change of slope occurs at 150 K with a more rapid decrease below. The anisotropy is not as prominent in T-1(-1)(T). The hyperfine coupling constant exhibits a cross-over behaviour from one linear regime of K(T) vs. chi(T) to another around a characteristic temperature. (c) 2005 Elsevier B.V. All rights reserved.