Influence of double occupancy and lattice distortions on the magnetic phase diagram ofA1−xAx′MnO3

Abstract

A model is presented that describes the competition between the ferromagnetic and several antiferromagnetic structures observed in the A{sub 1{minus}x}A{sub x}{sup {prime}}MnO{sub 3} series. It is found that the strong asymmetry of the magnetic phase diagram, i.e., predominantly ferromagnetic for x{lt}0.5 and antiferromagnetic for x{gt}0.5, can readily be explained by extending the double exchange model to include double occupancy. The strong charge fluctuations between different MnO{sub 6} clusters are the result of the charge-transfer-like nature of the manganites. The dependence of the magnetic structure on lattice distortions is described. The appearance of different magnetic structures around x=0.5 is interpreted in terms of changes in the Mn-O-Mn bond angle and the Jahn-Teller distortions. {copyright} {ital 1999} {ital The American Physical Society}