FRACTIONAL POWER TIME-DEPENDENCE OF THE NUCLEAR MAGNETIZATION IN THE PRESENCE OF PARAMAGNETIC IMPURITIES

We extend the theory of growth of the nuclear magnetization in the pre sence of paramagnetic impurities and the absence of spin diffusion to the case of multi-paramagnetic centers. We show that for short times a fter saturation pulses, the rate of growth of the magnetization is pro portional to t(alpha) where t is the time and alpha = 1/3, 1/2 and 2/3 for one-, two- and three-dimensional systems, respectively. We also p resent experimental data for which the total time-dependent magnetizat ion is proportional to exp[-(t/T-1)(alpha)], which reduces to the abov e time dependence for short times.