Theory of manganites: key role of intrinsic inhomogeneities

In recent years a variety of studies of models for manganites, mainly computationally, have shown the presence of electronic phase separation in the phase diagram. This tendency is expected to contribute to the formation of inhomogeneities in the real materials, at a nanometer scale. In order to explain the recently observed micrometer size coexisting clusters in some compounds, a new proposal is here described. It is based on the introduction of disorder in regions of parameters where the competing ferromagnetic and charge-ordered states are separated by first-order transitions. The coexisting clusters have the same charge, and its size is regulated by the strength of the disorder. Results are illustrated with the use of the random-field Ising model. The idea is general and should apply not only to manganites but to other compounds as well