11B NMR and relaxation in the MgB2 superconductor -: art. no. 012514

B-11 NMR and nuclear-spin-lattice relaxation rate (NSLR) are reported at 7.2 T and 1.4 T in powder samples of the intermetallic compound MgB2 with the superconducting transition temperature in zero field T-c = 39.2 K. From the first-order quadrupole perturbed NMR spectrum a quadrupole coupling frequency of 835 +/- 5 kHz is obtained. The Knight shift is very small and it decreases to zero in the superconducting phase. The NSLR follows a linear law with T1T = 165 +/- 10 (sec K). The results in the normal phase indicate a negligible s character of thr wave function of the conduction electrons at the Fermi level. Below T-c the NSLR is strongly field dependent indicating the presence of an important contribution related to the density and the thermal motion of flux lines. No coherence peak is observed at the lower field investigated (1.4 T).