A tight-band model is employed for the e2g-orbitals in manganites. It is shown that a large intraatomic Hund's coupling, JH and the resulting double-exchange mechanism lead to antiferromagnetic ordering along one of the cubic axis stabilized by the cooperative JT effect which further decreases the band energy of electrons. As a result, LaMnO3 is a band insulator built of 2D ferromagnetic layers. The critical concentration xc≃0.16, for onset of ferromagnetic and metallic behavior at low temperatures in La1−xSrxMnO3 and the phase transition are treated in the percolation approach.
@article{arxiv.cond-mat/9804328,
title = {Manganites at Low Temperatures and Light Doping:Band Approach and Percolation},
author = {Lev P. Gor`kov and Vladimir Z. Kresin},
journal= {arXiv preprint arXiv:cond-mat/9804328},
year = {2007}
}