Spectroscopic studies of inhomogeneous electronic phases in colossal magnetoresistance and charge-ordering compounds

Infrared reflectance and Raman spectroscopy measurements have been performed through the metal-semiconductor (or-semimetal) transitions of various "colossal magnetoresistance" and charge-ordering materials, including EuB₆ and the manganese perovskites. As described in this paper, our results demonstrate that these systems have phase regions characterized by electronic inhomogeniety of various types, including: (1) pure spin polarons, which form in a narrow temperature range above T_c in the "colossal magnetoresistance" system EuB₆; (2) magnetoelastic polarons, and an inhomogeneous ferromagnetic phase comprised of both metallic and insulating regions, in the "colossal magnetoresistance" regime of La_1-x(Sr, Ca)_xMnO₃ (x < 0.5); and (3) phase separation behavior involving coexisting ferromagnetic and antiferromagnetic domains in the intermediate-temperature (CO) phase of the charge-ordering system Bi_1-xCa_xMnO₃ (x > 0.5).