Electronic origin of magnetic and orbital ordering in insulating LaMnO3

We derive a spin-orbital model for insulating LaMnO3 which fulfills the SU( 2) symmetry of S=2 spins at Mn3+ ions. It includes the complete e(g) and t( 2g) superexchange which follows from a realistic Mn2+ multiplet structure i n cubic site symmetry, and the Jahn-Teller-induced orbital interactions. We show that the magnetic ordering observed in LaMnO3 is stabilized by a pure ly electronic mechanism due to the e(g) superexchange alone, and provides a unique and quantitatively correct explanation of the observed transition t emperature and the anisotropic exchange interactions. [S0163-1829(99)14901- 4].