MANGANITES AT LOW-TEMPERATURES AND LIGHT DOPING - BAND APPROACH AND PERCOLATION

A tight-band model is employed for the e(2g) orbitals in manganites. I t is shown that a large intra-atomic Hund coupling J(H) and the result ing double-exchange mechanism lead to antiferromagnetic ordering along one of the cubic axes, stabilized by the cooperative Jahn-Teller effe ct, which further decreases the band energy of the electrons. As a res ult, LaMnO3 is a band insulator built of 2D ferromagnetic layers. The critical concentration (x(c) similar or equal to 0.16) for the onset o f ferromagnetic and metallic behavior at low temperatures in La1-xSrxM nO3 and the phase transition are treated in a percolation approach. (C ) 1998 American Institute of Physics. [S0021-3640(98)01811-8].