B-11 NMR in YbNi2B2C single crystals: Crossover from localized moments to Fermi-liquid behavior

Data of B-11 NMR in a single crystal of YbNi2B2C are reported in the temperature range 1.7-300 K and for two orientations of the external magnetic field with respect to the tetragonal c axis of the crystal. For T > 50 K both the Knight shift K and the nuclear spin-lattice relaxation rate T-1(-1) can be accounted for by the presence of localized 4f moments at the Yb3+ site which polarize the conduction electrons via the Ruderman-Kittel-Kasuya-Yosida mechanism. On the other hand, at low temperatures, T < 5 K, the relaxation rate T-1(-1) obeys a Korringa-like law with a constant value of T1T typical of a normal metal with high density of states at the Fermi level and no localized moments.