We report an optical reflectivity study of charge and spin ordering in Bi1-xCaxMnO3 (x = 0.74 and 0.82) single crystals. In the high temperature phase, T > Tco, which is characterized by ferromagnetic correlations, the low-energy contribution to the optical conductivity σ1(ω) is dominated by small polaron dynamics. For Tco > T > TN, the presence of both small polaron and charge-gap-like features signifies "phase separation" behavior in which domains of ferromagnetic and antiferromagnetic order coexist. Below TN, the polaron response is completely suppressed, and a complete charge gap develops, coincident with the onset of long-range antiferromagnetic order.
ASJC Scopus subject areas
- Physics and Astronomy(all)