Effective Hamiltonian for an extended Kondo-lattice model and a possible origin of charge ordering in half-doped manganites

An effective Hamiltonian is derived in the case of the strong Hund coupling and on-site Coulomb interaction by means of a projective perturbation approach. A physical mechanism for charge ordering in half-doped manganites (R0.5X0.5MnO3) is proposed. The virtual process of electron hopping results in antiferromagnetic superexchange and a repulsive interaction, which may drive electrons to form a Wiener lattice. The phase diagram of the ground state of the model is presented at half doping. In the case of formation of a Wigner lattice, we prove that spins of electrons are aligned ferromagnetically as well as that the localized spin background is antiferromagnetic. The influence of the on-site Coulomb interaction is also discussed. [S0163-1829(99)01621-5].