  Ferri-/ferromagnetic exchange coupled composites are promising candidates for
bit patterned media because of the ability to control the magnetic properties
of the ferrimagnet by its composition. A micromagnetic model for the bilayer
system is presented where we also incorporate the microstructural features of
both layers. Micromagnetic finite element simulations are performed to
investigate the magnetization reversal behaviour of such media. By adding the
exchange coupled ferrimagnet to the ferromagnet, the switching field could be
reduced by up to $40\,\%$ and also the switching field distribution is
narrowed. To reach these significant improvements, an interface exchange
coupling strength of $2\,\mathrm{mJ/m^2}$ is required.
