  We investigate the possibility of superfluid/ferromagnet/superfluid
(SFS)-junction in a superfluid Fermi gas. To examine this possibility in a
simple manner, we consider an attractive Hubbard model at $T=0$ within the
mean-field theory. When a potential barrier is embedded in a superfluid Fermi
gas with population imbalance ($N_\uparrow>N_\downarrow$, where $N_\sigma$ is
the number of atoms with pseudospin $\sigma=\uparrow,\downarrow$), this barrier
is shown to be {\it magnetized} in the sense that excess $\uparrow$-spin atoms
are localized around it. The resulting superfluid Fermi gas is spatially
divided into two by this {\it ferromagnet}, so that one obtains a junction
similar to the superconductor/ferromagnet/superconductor-junction discussed in
superconductivity. Indeed, we show that the so-called $\pi$-phase, which is a
typical phenomenon in the SFS-junction, is realized, where the superfluid order
parameter changes its sign across the junction. Our results would be useful for
the study of magnetic effects on fermion superfluidity using an ultracold Fermi
gas.
