  In nanocomposite magnetic materials the exchange coupling between phases
plays a central role in the determination of the extrinsic magnetic properties
of the material: coercive field, remanence magnetization. Exchange coupling is
therefore of crucial importance in composite systems made of magnetically hard
and soft grains or in partially crystallized media including nanosized
crystallites in a soft matrix. It has been shown also to be a key point in the
control of stratified hard / soft media coercive field in the research for
optimized recording media. A signature of the exchange coupling due to the
nanostructure is generally obtained on the magnetization curve $M(H)$ with a
plateau characteristic of the domain wall compression at the hard/soft
interface ending at the depinning of the wall inside the hard phase. This
compression / depinning behavior is clearly evidenced through one dimensional
description of the interface, which is rigorously possible only in stratified
media. Starting from a local description of the hard/soft interface in a model
for nanocomposite system we show that one can extend this kind of behavior for
system of hard crystallites embedded in a soft matrix.
