  Heat assisted recording is a promising technique to further increase the
storage density in hard disks. Multilayer recording grains with graded Curie
temperature is discussed to further assist the write process. Describing the
correct magnetization dynamics of these grains, from room temperature to far
above the Curie point, during a write process is required for the calculation
of bit error rates. We present a coarse grained approach based on the
Landau-Lifshitz-Bloch (LLB) equation to model exchange coupled grains with low
computational effort. The required temperature dependent material properties
such as the zero-field equilibrium magnetization as well as the parallel and
normal susceptibilities are obtained by atomistic Landau-Lifshitz-Gilbert (LLG)
simulations. Each grain is described with one magnetization vector. In order to
mimic the atomistic exchange interaction between the grains a special treatment
of the exchange field in the coarse grained approach is presented.
