Abstract
The magnetic and orbital orders for the bilayer manganites in the doping region 0.5 < x < 1.0 have been investigated from a model that incorporates the two eg orbitals at each Mn site, the inter-orbital Coulomb interaction and lattice distortions. The usual double exchange operates via the eg orbitals. It is shown that such a model reproduces much of the phase diagram recently obtained for the bilayer systems in this range of doping. The C-type phase with (π,0,π) spin order seen by Ling et al. appears as a natural consequence of the layered geometry and is stabilised by the static distortions of the system. The orbital order is shown to drive the magnetic order while the anisotropic hopping across the eg orbitals, the layered nature of the underlying structure and the associated static distortions largely determine the orbital arrangements.