Electronic and magnetic properties of single-crystal YNi2B2C from 11B and 89Y NMR and magnetic-susceptibility measurements

The quaternary intermetallic compound superconductor YNi2B2C with transition temperature Tc=15.5 K has been investigated by 11B and 89Y nuclear magnetic resonance (NMR) and by magnetic susceptibility χ measurements both in the normal and the superconducting states. The NMR and relaxation measurements have been performed in a powder sample and single crystals. 11B (I=3/2) NMR spectra display patterns typical for an axially symmetric field gradient with quadrupole coupling frequency vQ=698±1 kHz and 89Y (I=1/2) data show spectra typical for a large anisotropic Knight shift, K, with axial symmetry (3Kax=0.042%). In the normal state, the 11B K increases with decreasing temperature while 89Y K decreases. The temperature dependences of both the isotropic (Kiso) and anisotropic (3Kax) components of the 11B and 89Y Knight shifts are presented together with dc magnetic susceptibility (χ) measurements obtained from magnetization measurements and are explained by the sharp features of the density of states near the Fermi level in the system. The analysis of the NMR and χ(T) data when combined with the theoretical calculation of the Van Vleck contribution to χ(T) allows the determination of the hyperfine coupling constants for both nuclei investigated and permits the separation of the different contributions to the total measured χ(T). The nuclear spin-lattice relaxation rate (NSLR) (T-11) results for 11B show an enhancement of (T1T)-1 when lowering the temperature, consistent with previous results. (Abstract Truncated)