Spin and orbital ordering in double-layered manganites

We study theoretically the phase diagram of the double-layered perovskite manganites taking into account the orbital degeneracy, the strong Coulombic repulsion, and the coupling with the lattice deformation. Observed spin structural changes such as increased doping, are explained in terms of the orbital ordering and the bond-length dependence of the hopping integral along the c axis. Temperature dependence of the neutron diffraction peak corresponding to the canting structure is also explained. Comparison with the three-dimensional cubic system is made.