  By using the projection operator technique it is observed that the strong
Hund's rule coupling and s-d interaction in transition metal elements may lead
to an effective coupling between the spin current and spin spirality. As a
result, the spin spirality can be regarded as a driving force to produce a spin
current. The spin current may give rise to a novel type of field acting on the
spins. A spin battery is designed based on the interactions between the spin
current and spin spirality.
