Magnetoelectronic and Magnetostructural Coupling in the La 1 - x Ca x MnO 3 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 CaMnO 3 and LaMnO 3 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 (La 3+ , Ca 2+ ) 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.