The spin-diffusion effect in the dipolar ordering state

The theory of spin diffusion is extended to the case of nuclear dipolar ord er in solids containing paramagnetic impurities. We show that at the beginn ing of the relaxation process the relaxation function of the dipolar order is non-exponential, due to the direct interaction with paramagnetic impurit ies, and proceeds to become an exponential function of time, when spin diff usion of the dipolar order takes place. Using experimental data on these tw o relaxation regimes in CaF2 doped with Mn2+, the diffusion coefficient and the radius of the diffusion barrier were estimated.