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

摘要

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 EuB{sub}6 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 T{sub}c in the "colossal magnetoresistance" system EuB{sub}6; (2) magnetoelastic polarons, and an inhomogeneous ferromagnetic phase comprised of both metallic and insulating regions, in the "colossal magnetoresistance" regime of La{sub}(1-x)(Sr,Ca){sub}xMnO{sub}3 (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{sub}(1-x)Ca{sub}xMnO{sub}3 (x> 0.5).