Phase Diagram in R1−xAxMnO3

We study the phase diagram of R1−xAxMnO3 (R=La, Pr, Nd, Sm ; A=Ca, Sr, Ba) by taking into account the degeneracy of eg orbitals and the anisotropy of the transfer integral. The electron-electron interaction is treated in the mean field approximation with the optimization of the spin and orbital structures. The global phase diagram is understood in terms of the two interactions, i.e., the super exchange interaction for small x and the double exchange interaction for larger x modified by the orbital degeneracy. The dimensionality of the electronic energy band resulting from the orbital structure is essential to determine the phase diagram. The effects of the Jahn-Teller distortion are also studied. 71.27.+a, 71.30.+h, 75.30.Et Typeset using REVTEX