Simulations of fast switching in exchange coupled longitudinal thin-film media

We have developed a Langevin dynamic simulation of high speed switching in longitudinal thin-film media. The model assumes a randomly placed set of gr ains with a particle size distribution which interact via magnetostatic and exchange fields. The dynamic properties of the material are simulated usin g the Langevin dynamic formalism which is essentially the Landau-Lifshitz-G ilbert equation of motion augmented by a random field whose properties are determined by the fluctuation-dissipation theorem. We have simulated pulsed -field magnetization and remanence curves which are obtained by applying a field pulse to a system in the remanent magnetization state. Calculations o f the time dependence of the magnetization, and the time dependence of the coercivity have been made. The high frequency dynamic behavior of the syste ms is found to be strongly dependent on the value of the exchange coupling between the grains. (C) 1999 American Institute of Physics. [S0021-8979(99) 62708-6].