Magnetic phases of electron-doped manganites

We study the anisotropic magnetic structures exhibited by electron-doped manganites using a model which incorporates the double exchange between orbitally degenerate eg electrons and the superexchange between t2g electrons with realistic values of the Hund's coupling (JH), the superexchange coupling (JAF), and the bandwidth $(W).$ We look at the relative stabilities of the G-, C-, and A-type antiferromagnetic phases. In particular we find that the G phase is stable for low electron doping as seen in experiments. We find good agreement with the experimentally observed magnetic phase diagrams of electron-doped manganites $(x>0.5)$ such as Nd_1-xSrₓMnO₃, Pr_1-xSrₓMnO₃, and Sm_1-xCaₓMnO₃. We can also explain the experimentally observed orbital structures of the C and A phases. We also extend our calculation for electron-doped bilayer manganites of the form R_2-2xA₁₊₂ₓMn₂O₇ and predict that the C phase will be absent in these systems due to their reduced dimensionality.