${}^{11}\mathrm{B}$ NMR and relaxation in the ${\mathrm{MgB}}_2$ superconductor

${}^{11}\mathrm{B}$ 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 ${\mathrm{MgB}}_2$ with the superconducting transition temperature in zero field $T_c=39.2\mathrm{}\hspace{0.5em}\mathrm{K}.$ From the first-order quadrupole perturbed NMR spectrum a quadrupole coupling frequency of $835\pm 5\hspace{0.5em}\mathrm{kHz}$ is obtained. The Knight shift is very small and it decreases to zero in the superconducting phase. The NSLR follows a linear law with $T_{1}T=165\mathrm{}\pm 10\hspace{0.5em}\left(\sec \mathrm{}\mathrm{K}\right).\mathrm{}$ The results in the normal phase indicate a negligible s character of the 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).