NMR EXCITATION AND RELAXATION IN A SINGLE DOMAIN SPIN-GLASS

Zero field NMR measurements of the spin lattice relaxation time T1 on copper satellite nuclei in a frozen CuMn "single domain" spin glass show that the longitudinal nuclear magnetization recovery is not purely exponential. Three possible causes for the observed nonexponentiality have been considered: The distribution of enhancement factors, the differences in neighbourhood experienced by the satellite nuclei and a small quadrupole splitting of Zeeman levels. The latter is shown to be the suitable mechanism. The longitudinal magnetization recovery of silver satellite nuclei in AgMn, i.e. in the absence of a quadrupole splitting, was purely exponential. Applying the Redfield theory of relaxation times a comparison of T1 and T2 shows that the components of the spectral density function of the fluctuating magnetic field are anisotropic.