SPIN RELAXATION FOR MOTION RESTRICTED TO 2 DIMENSIONS

The sources of the logarithmic frequency dependence in the NMR spin-la ttice relaxation rate for systems with two-dimensionally restricted mo tion have been studied. In such systems, a spin moves on a plane and r elaxes via dipole-dipole interactions with either stationary or moving spins, either of which may be in the same plane or on different plane s from the relaxing spins. On simple physical grounds, both intraplana r and interplanar interactions are expected to contribute to logarithm ically divergent relaxation, contrary to previous numerical results wh ere no interplanar component was found. The present lattice sum calcul ations of the contributions to the logarithmic dependence for both int erplanar and intraplanar interactions confirm that interplanar contrib utions are nonzero. However, the interplanar contributions fall off ex tremely rapidly with increasing separation of the planes and so are no t likely to play an important role for most systems. As an example, th e interplanar and intraplanar contributions to the observed divergent relaxation in ZrBe2H1.4 are compared. [S0163-1829(98)01825-6].