  A method, based on the Neel-Brown model of thermally activated magnetization
reversal of a magnetic single-domain particle, is proposed to study the field
sweep rate dependence of the coercive field of single-molecule magnets (SMMs).
The application to Mn12 and Mn84 SMMs allows the determination of the important
parameters that characterize the magnetic properties: the energy barrier, the
magnetic anisotropy constant, the spin, tau_0, and the crossover temperature
from the classical to the quantum regime. The method may be particularly
valuable for large SMMs that do not show quantum tunneling steps in the
hysteresis loops.
