Effect of orbital ordering on the magnetic-structure formation in the LaMnO3 Jahn-Teller magnet

A study is reported on the relation between orbital ordering and the magnet ic structure of an LaMnO3 crystal. The dependence of the exchange parameter s on the orbital-structure angle Phi has been determined. Inclusion into th e spin Hamiltonian of isotropic exchange interaction and single-ion anisotr opy, which depends on the angle Phi and rotational distortions, results in a four-sublattice structure (A(X), F-Y, G(Z)), with the sublattice magnetic moments oriented close to the long axis of the orthorhombic cell in the ba sal plane of the crystal (A(X) >> G(Z), F-Y). The effect of the rare-earth- ion size in RMnO3 manganites on the orbital and magnetic structures is cons idered. (C) 2000 MAIK "Nauka /Interperiodica".