  The low temperature relaxation of the magnetization in magnetic molecular
solids such as Fe$_8$ is studied using Monte Carlo simulations. A set of rate
equations is developed to understand the simulations, and the results are
compared. The simulations show that the magnetization of an initially saturated
samples deviates as a square-root in time at short times, as observed
experimentally, and this law is derived from the rate equations analytically.
