PROBING ANISOTROPIC MAGNETOTRANSPORT IN MANGANESE PEROVSKITES USING RAMAN-SPECTROSCOPY

We report an electronic Raman scattering study of the colossal magneto resistance (CMR) manganese perovskites as a function of temperature, m agnetic field, symmetry, and doping. The low-frequency electronic Rama n 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 sta te. We found that the B-1g-symmetry electronic scattering intensity is significantly reduced with applied magnetic field near T-C, in a mann er reminiscent of the de magnetoresistivity. The strongly field-depend ent 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, p erhaps consisting of both metallic and insulating components. [S0163-1 829(98)51640-2].