Phase Diagram in R_{1-x}A_xMnO_3

Abstract

We study the phase diagram of R_{1-x}A_xMnO_3 (R=La, Pr, Nd, Sm ; A=Ca, Sr, Ba) by taking into account the degeneracy of $e_g$ 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.