  We show a perturbation theory of the Josephson transport through
ferromagnetic insulators (FIs). Recently we have found that the appearance of
the atomic scale 0-pi transition in such junctions based on numerical
calculations. In order to explore the mechanism of this anomalous transition,
we have analytically calculated the Josephson current using the tunneling
Hamiltonian theory and found that the spin dependent pi-phase shift in the FI
barrier gives the atomic scale 0-pi transition.
