${}^{11}\mathrm{B}$ NMR in ${\mathrm{YbNi}}_2{\mathrm{B}}_2\mathrm{C}$ single crystals: Crossover from localized moments to Fermi-liquid behavior

Data of ${}^{11}\mathrm{B}$ NMR in a single crystal of ${\mathrm{YbNi}}_2{\mathrm{B}}_2\mathrm{C}$ 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 $T>\mathrm{}50\mathrm{}\mathrm{K}$ 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 ${\mathrm{Yb}}^{3+}$ site which polarize the conduction electrons via the Ruderman-Kittel-Kasuya-Yosida mechanism. On the other hand, at low temperatures, $T<\mathrm{}5\mathrm{}\mathrm{K},$ the relaxation rate $T_1^{-1}$ obeys a Korringa-like law with a constant value of $T_{1}T$ typical of a normal metal with high density of states at the Fermi level and no localized moments.