NMR excitation and relaxation in a “single domain” spin glass

Abstract

Zero field NMR measurements of the spin lattice relaxation time T 1 on copper satellite nuclei in a frozen Cu Mn “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 Ag Mn, i.e. in the absence of a quadrupole splitting, was purely exponential. Applying the Redfield theory of relaxation times a comparison of T 1 and T 2 shows that the components of the spectral density function of the fluctuating magnetic field are anisotropic.