  In view of recent experiments, indicating the spatial coexistence of
conducting and insulating regions in the ferromagnetic metallic phase of doped
manganites, we propose a refined mixed-phase description. The model is based on
the competition of a double-exchange driven metallic component and a polaronic
insulating component, whose volume fractions and carrier concentrations are
determined self-consistently by requiring equal pressure and chemical
potential. The resulting phase diagram as well as the order of the phase
transition are in very good agreement with measured data. In addition,
modelling the resistivity of the mixed, percolative phase by a random resistor
network, we obtain a pronounced negative magnetoresistance in the vicinity of
the Curie temperature $T_C$.

Strongly Correlated Electrons