Stability of the magnetic phase in half-doped manganites

The stability of the magnetic phase of quarter-filled manganites was studied using the two-orbital double-exchange model with the effect of lattice distortion and Coulomb repulsion in a mean field approximation for two-dimensional systems. A magnetic phase diagram is depicted in a plane of the lattice distortion and the superexchange interaction between localized t(2g) spins. When the ratio of the superexchange interaction to the hopping integral is small, a ferromagnetic ground state with d(x2-y2) orbital ordering is stabilized, With increases in the ratio, the ferromagnetic ground state changes to a charge-ordered CE type antiferromagnetic state irrespective of the lattice distortion. The respective roles of the carious ingredients included in the model are discussed, and theoretical and experimental results are compared. We also discuss die effects of Fe and Cr substitution for Mn ions with regards to the stability of the CE phase.