ELECTRONIC AND MAGNETIC-PROPERTIES OF SINGLE-CRYSTAL YNI2B2C FROM B-11 AND Y-89 NMR AND MAGNETIC-SUSCEPTIBILITY MEASUREMENTS

The quaternary intermetallic compound superconductor YNi2B2C with tran sition temperature T-c = 15.5 K has been investigated by B-11 and Y-89 nuclear magnetic resonance (NMR) and by magnetic susceptibility chi m easurements both in the normal and the superconducting states. The NMR and relaxation measurements have been performed in a powder sample an d single crystals. B-11 (I = 3/2) NMR spectra display patterns typical for an axially symmetric field gradient with quadrupole coupling freq uency upsilon(Q) = 698 +/- 1 kHz and Y-89 (I = 1/2) data show spectra typical for a large anisotropic Knight shift, K, with axial symmetry ( 3K(ax) = 0.042%). In the normal state, the B-11 K increases with decre asing temperature while Y-89 K decreases. The temperature dependences of both the isotropic (K-iso) and anisotropic (3K(ax)) components of t he B-11 and Y-89 Knight shifts are presented together with de magnetic susceptibility (chi) measurements obtained from magnetization measure ments 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 chi(T ) data when combined with the theoretical calculation of the Van Vleck contribution to chi(T) allows the determination of the hyperfine coup ling constants for both nuclei investigated and permits the separation of the different contributions to the total measured X(T) The nuclear spin-lattice relaxation rate (NSLR) (T-1(-1)) results for B-11 show a n enhancement of (T1T)(-1) when lowering the temperature, consistent w ith previous results. It is shown that the enhancement of the B-11 NSL R is not due to the effects of antiferromagnetic fluctuations of Ni ma gnetic moments but simply due to the increase of the s-band spin susce ptibility with decreasing temperature as reflected in the temperature dependence of the Knight shift. Contrary to the case of B-11, the Y-89 NSLR displays a (T1T)(-1) which is independent of temperature, indica ting that the dominant contribution is from a large temperature-indepe ndent orbital Knight shift. In the superconducting state, the B-11 NSL R drops rapidly without a coherence peak and is found to fit BCS behav ior with a superconducting gap parameter at T = 0 given by 2 Delta(0) = (3.4 +/- 0.5)k(B)T(c).