A Localized-Electron to Collective-Electron Transition in the System (La, Sr)CoO3

Abstract

Crystallographic, magnetic, and electrical studies of the system La1−xSrxCoO3.00±0.01 for 0≤x≤0.5 give indirect evidence for the presence of chemical inhomogeneities separating strontium-free regions, where localized ``3d'' electrons occur at thermally excited high-spin Co3+ ions, from strontium-rich regions, where the ``3d'' electrons are collective and give ferromagnetism at low temperatures. These different regions occur within the same rhombohedral perovskite crystal and appear to represent two different electronic phases within the same crystallographic phase. A schematic band model for the ferromagnetic phase is presented.