Crucial role of Jahn-Teller distortions in LaMnO(3)

The crucial role of the cooperative Jahn-Teller deformations in determining the magnetic properties of stoechiometric LaMnO(3) is studied by means of exact diagonalization. The layered antiferromagnetic order mainly results from the strong cooperative Jahn-Teller deformations, stabilizing a certain type of orbital ordering. The main result is that antiferromagnetic (ferromagnetic) coupling along the c-direction (ab-planes) call be understood only if the Jahn-Teller energy is much larger than the superexchange couplings, which is consistent with experiments. The crucial role of the deformation anisotropy Q(2)/Q(3) is also emphasized: realistic values of Q(2)/Q(3) are needed to stabilize the layered order. The experimental values of the superxchange couplings can be recovered using reasonable sets of parameters. RI Grilli, Marco/C-6309-2009