Magnetoelectronic and magnetostructural coupling in the La1-xCaxMnO3 system.

Phenomenological models of the colossal magnetoresistance,, manganites have emphasized a local picture for the Mn ion, and little attention has been given to the effects of Mn d-O p hybridization. We present self-consistent local spin-density electronic-structure studies that properly account for hybridization, and find that the very different structural and antiferromagnetic symmetries of the ground states of CaMnO3 and LaMnO3 are obtained. In the CMR regime ferromagnetic coupling is preferred, as observed, and strongly hybridized bands leading to a partially open-shell oxygen ion in the majority channel accounts for good metallic conduction at low temperature. Strong local environment effects on the Mn ion arising from cation charge differences (La3+, Ca2+) suggest Anderson localization of the low density of minority carriers, leading to half-metallic regions. This feature, together with strong spin dependence of covalent hybridization, may provide the mechanism for the semiconducting behavior at high temperature.