Magnetic and orbital ordering in electron-doped manganites

The total energies for various magnetic structures of R 1 - x A x MnO 3 (R = La, Nd, Pr, Sm, A = Ca, Ba, Sr) are evaluated using energy bands E(k) accounting for the orbital degeneracy of eg band of manganese for the two-sublattice A, C, and G types of spin and orbital orders in the region x>0.5. To determine the magnetic and orbital configurations, minimization of the ground-state energy with respect to the interspin angle of Mn 4 + ions and the intro-atomic-orbital mixing angles of the two sublattices has been performed. In the case of the degenerate eg level, the calculated magnetic phase diagrams fail to explain the experimentally observed arrangement of magnetic phases. The account of e g -level splitting stabilizes the magnetic phases with the consistent orbital ordering compatible with experimental observations. Besides, the tendency of phase separation, not only for the G phase but also for the collinear C phase in the low-doping region is revealed resulting from the e g -splitting dependence on doping.