Manganites at low temperatures and light doping: band approach and percolation

A tight-band model is employed for the e(2g) orbitals in manganites. It is shown that a large intra-atomic Hund coupling J(H) and the resulting double-exchange mechanism lead to antiferromagnetic ordering along one of the cubic axes, stabilized by the cooperative Jahn-Teller effect, which further decreases the band energy of the electrons. As a result, LaMnO3 is a band insulator built of 2D ferromagnetic layers. The critical concentration (x(c) similar or equal to 0.16) for the onset of ferromagnetic and metallic behavior at low temperatures in La1-xSrxMnO3 and the phase transition are treated in a percolation approach. (C) 1998 American Institute of Physics. [S0021-3640(98)01811-8].