Probing anisotropic magnetotransport in manganese perovskites using Raman spectroscopy

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 de 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 much less than T-C, suggesting that the ferromagnetic phase is inhomogeneous, perhaps consisting of both metallic and insulating components. [S0163-1829(98)51640-2].