Raman Scattering Studies of Single-Crystal La1−xSrxMnO3

We present the results of Raman scattering studies of single-crystal La1-xSrxMnO3 (x = 0.05, 0.10, 0.15, 0.20, 0.25, and 0.35) as a function of doping and in the temperature range 10–300 K. The room-temperature Raman spectrum of the x = 0.05 compound displays four phonon bands near ～ 260, 488, 612, and 674 cm^−1. With increasing Sr doping, and a corresponding structural phase transition from an orthorombic to a rhombohedral form, there is a broadening of the linewidths and a decrease in intensities of these phonon modes. When the temperature is lowered, for the x = 0.05 material, two low-frequency phonons associated with the out-of-phase rotation and internal bending of MnO6 octahedra show a noticeable hardening below the canted anti-ferromagnetic transition, which is an evidence for strong spin-phonon coupling. Interestingly, this anomalous behavior disappears in the higher Sr doping level.