Interplay between orbital, charge and magnetic orderings in R1-xAxMnO3 (x=0, 0.5)

This work is devoted to the description of the orbital and magnetic structures of pure and charge-ordered manganites, caused by crystal and charge structures and the Jahn-Teller effect. The model under consideration is based on the orbital dependency of the magnetic interactions in Jahn-Teller crystal. The orbital structure is considered dependent upon the Jahn-Teller distortions of the coordination of the Mn3+ ions and upon the crystal field. It is shown that exchange interactions forming the magnetic structure of the charge-ordered manganite could be described in the superexchange approximation because of localization of the charge carriers. For pure manganite and for charge-ordered phase, the exchange parameters dependencies and the single-ion anisotropy dependency, upon the angle of orbital states mixing, are drawn. Therefore, it is shown that the orbital structure of the charge-ordered phase is formed mainly by cooperative Jahn-Teller distortions and, taking into account the charge superstructure, causes the non-trivial magnetic structure. (C) 2001 Elsevier Science B.V. All rights reserved.