Spin lattice relaxation of spin‐½ nuclei in solids containing diluted paramagnetic impurity centers. I. Zeeman polarization of nuclear spin system

Abstract

AbstractSpin‐lattice relaxation mechanisms of nuclear spins in solids in the presence of low concentrations of paramagnetic centers are discussed. Apart from the electron spin‐lattice relaxation mechanism, three‐spin processes involving two electron spins and a nuclear spin may also play a role in the spin‐lattice relaxation of the nuclear spins. Nuclear spins that are close to a paramagnetic impurity center experience large local fields and do not contribute to the NMR signal. Only a small percentage of nuclear spins surrounding an impurity center are polarized directly. The majority of the nuclear spins are polarized by spin diffusion, which is a slow process. A brief overview of a number of paramagnetic impurity centers, which are common in natural diamond, is given and experimental 13C spin‐lattice relaxation times for a suite of natural diamonds are compared with calculated values. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson 19A: 20–35, 2003.