  We study the Josephson-like spin currents between two ferromagnetic metals by
deriving the effective action of the junction. A DC spin Josephson current with
the full O(3) symmetry is obtained. By the analogy to the superconducting
junctions, we have shown that a time-independent uniform magnetic field can
serve as the source of the AC spin Josephson effect. That is, the spin current
becomes a periodic function of the time with the period proportional to the
inverse of the magnitude of the external magnetic field.
