Thermal induced reversal in coupled grains and elongated particles

A method has been developed to analyze thermal fluctuations in systems with a nonuniform magnetization reversal. The application is to either interacting single domain particles or elongated grains where the magnetization can reverse nonuniformly. In our approach, the stochastic differential equations are obtained by adding damping and thermal fluctuations consistent with the fluctuation-dissipation theorem to each independent mode of the interacting system around equilibrium. The collective thermal reversal mode is obtained from the optimal path of a weakly thermal agitated system. Asymptotic analysis gives the first mean exit time formula for the long time thermal excitation region. Examples of 2:1 and 5:1 aspect ratio particles are given. (C) 2002 American Institute of Physics.