PHASE SEPARATION IN SYSTEMS WITH CHARGE ORDERING
Kagan M.Yu., Kugel K.I., Khomskii D.I.

Received: December 25, 2000

PACS: 71.45.Lr, 75.10.-b, 75.30.Mb, 75.30.Kz

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A simple model of charge ordering is considered. It is explicitly shown that at any deviation from half-filling (n eq 1/2), the system is unstable with respect to the phase separation into the charge-ordered regions with n = 1/2 and metallic regions with a smaller electron or hole density. A possible structure of this phase-separated state (metallic droplets in a charge-ordered matrix) is discussed. The model is extended to account for the strong Hund-rule onsite coupling and the weaker intersite antiferromagnetic exchange. The analysis of this extended model allows us to determine the magnetic structure of the phase-separated state and to reveal the characteristic features of the manganites and other substances with charge ordering.