Time relaxation of interacting single-molecule magnets -: art. no. 094431

We study the relaxation of interacting single-molecule magnets in both spatially ordered and disordered systems. The tunneling window is assumed to be, as in Fe-8, much narrower than the dipolar field spread. We show that relaxation in disordered systems differs qualitatively from relaxation in fully occupied cubic and Fe-8 lattices. We also study how line shapes that develop in "hole-digging" experiments evolve with time t in these fully occupied lattices. We show (1) that the dipolar field h scales as t(p) in these hole line shapes and (2) how p varies with lattice structure. Line shapes are not, in general, Lorentzian. More specifically, in the lower portion of the hole, they behave as (vertical bar h vertical bar/t(p))((1/p)-1) if h is outside the tunnel window. This is in agreement with experiment and with our own Monte Carlo results.