  Ground state properties of the Kondo model for manganese oxides in one
dimension are studied using numerical techniques. The large Hund coupling
($J_{H}$) limit is specially analyzed. A robust region of fully saturated
ferromagnetism (FM) is identified at all densities. For open boundary
conditions it is shown exactly that the ground state is FM at $J_{H} = \infty$.
Hole-spin phase separation competing with FM was also observed when a large
exchange $J$ between the $Mn^{3+}$ ions is used. As the spin of the transition
metal ion grows, the hole mobility decreases providing a tentative explanation
for the differences between Cu-oxides and Mn-oxides.

Condensed Matter