Magnetic polarons in materials with colossal magnetoresistance

We construct a phase diagram for the materials with colossal magnetoresista nce. The basic model which describes these materials is a double-exchange m odel. We rigorously prove that a ground state of this model corresponds to a phase-separated state with small ferromagnetic polarons inside an antifer romagnetic matrix. The general picture of a percolative state, which emerge s from our calculations, is in good agreement with recent experiments on do ped manganites. (C) 2000 Elsevier Science B.V. All rights reserved.