Double-exchange model with background superexchange interactions: Phase diagrams ofLa1−xAxMnO3manganites

Abstract

The phase diagram of the double exchange model for manganites with ferromagnetic Hund coupling and antiferromagnetic superexchange coupling between ${t}_{2g}$ electrons is investigated by using Monte Carlo methods in low dimensions. Extensive calculations are performed for the one- and two-dimensional lattice model where the localized spins of ${t}_{2g}$ electrons are treated as classical spins. While the results for the model with no antiferromagnetic superexchange interaction are in good agreement with the recent work by Dagotto and co-workers, the regions of phase separations are found to occur both at large and low electron densities in the phase diagram with background superexchange couplings. In addition, it is noted that the ground state is changed from ferromagnetic to antiferromagnetic state for the larger antiferromagnetic superexchange interaction at quarter filling.