  We present a micromagnetic approach to exchange bias (EB) in ferromagnetic
(FM)/antiferromagnetic (AFM) thin film systems with a small number of
irreversible interfacial magnetic moments. We express the exchange bias field
$H_{EB}$ in terms of fundamental micromagnetic length scale---the exchange
length $l_{ex}$. The benefit from this approach is a better separation of a
term related to FM layer from a term related to FM/AFM coupling at interfaces.
Using this approach we estimate the highest limit of $H_{EB}$ in real FM/AFM
systems.
