  Microwave assisted magnetization reversal are studied in the bulk bilayer
exchange coupled system. We investigate the nonlinear magnetization reversal
dynamics in a perpendicular exchange spring media using Landau-Lifshitz
equation. In the limit of the infinite thickness of the system, the propagation
field leads the reversal of the system. The reduction of the switching field
and the magnetization profile in the extended system are studied numerically.
The possibility to study the dynamics analytically is discussed and an
approximation where two P-modes are coupled by an interaction field is
presented. The ansatz used for the interaction field is validated by comparison
with the numerical results. This approach is shown to be equivalent to two
exchange coupled macrospins.
