Phase separation, charge ordering and electron transport in manganites

A simple model of charge ordering is considered. It takes into account both the Coulomb repulsion at neighboring sites and the essential magnetic interactions. It is shown explicitly that at any deviation from half-filling (n not equal 1/2) the system is unstable with respect to phase separation into charge ordered regions with n = 1/2 and metallic regions with smaller electron or hole density. Possible structure of this phase-separated state (metallic droplets in a charge-ordered matrix) is discussed. We estimate the parameters of these droplets and construct the phase diagram reproducing the main features observed in real manganites. The conductivity and noise spectrum for this phase-separated state are also discussed. (C) 2001 Elsevier Science B.V. All rights reserved.