Within a model of the coherent rotation, we assume underdamped dynamics of magnetization in single-domain ferromagnetic particles and calculate the prefactor ${\mathit{f}}_0$(h) of the thermal decay rate as a function of the applied field h. Four different models of dissipative coupling are considered. As opposed to the previously reported temperature dependence of the prefactor, the field dependence is remarkably independent of the chosen coupling mode. The prefactor ${\mathit{f}}_0$(h) drops off sharply as h approaches the nucleation field and significantly enhances the coercivity whose model calculation, together with that of the switching-field distribution, is carried out.

• Received 25 June 1993

DOI:https://doi.org/10.1103/PhysRevB.48.15823