We report an electronic Raman scattering study of the colossal magnetoresistance (CMR) manganese perovskites as a function of temperature, magnetic field, symmetry, and doping. The low-frequency electronic Raman spectrum in the paramagnetic-insulating phase of these materials is characterized by a diffusive Raman-scattering response, while a nearly flat continuum response is observed in the ferromagnetic-metallic state. We found that the $B_{1g}$-symmetry electronic scattering intensity is significantly reduced with applied magnetic field near $T_C,$ in a manner reminiscent of the dc magnetoresistivity. The strongly field-dependent scattering rate in the $B_{1g}$ channel appears to reflect the highly field-dependent mobility along the Mn-O bond direction expected in the double exchange mechanism. In addition, we observe a persistent field dependence in the $B_{1g}$ electronic scattering response for $T\ll T_C,$ suggesting that the ferromagnetic phase is inhomogeneous, perhaps consisting of both metallic and insulating components.

• Received 24 April 1998

DOI:https://doi.org/10.1103/PhysRevB.58.R10115