Low-temperature magnetization relaxation in magnetic molecular solids

•A novel set of non-linear rate equations for the coupled evolution of the magnetization and dipole field distribution.•An analytic derivation of the short-time square root in time behavior of the magnetization relaxation.•Agreement between theory and simulations without further fitting parameters.

The low temperature relaxation of the magnetization in molecular magnetic solids such as Fe8 is studied using Monte Carlo simulations. A set of rate equations is then developed to understand the simulations, and the results are compared. The simulations show that the magnetization of an initially saturated sample deviates as a square-root in time at short times, as observed experimentally, and this law is derived from the rate equations analytically.