Spectroscopic Studies of Inhomogeneous Electronic Phases in Colossal Magnetoresistance and Charge-Ordering Compounds

Abstract

AbstractInfrared 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 inhomogeneity of various types, including: (1) pure spin polarons, which form in a narrow temperature range above Tc 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 La1−x(Sr,Ca)xMnO3 (x < 0.5); and (3) phase separation behavior involving coexisting ferromagnetic and antiferromagnetic domains in the intermediatetemperature (CO) phase of the charge-ordering system Bi1−xCaxMnO3 (x > 0.5).