Effect of structural and magnetic transitions in La1-xMxMnO3 (M=Sr, Ca) single crystals in Raman scattering

Polarized Raman spectra of undoped and doped La1-xMxMnO3 single crystals have been studied in the temperature range from 5 to 423 K (M=Sr, Ca). The spectral intensity is mainly related to scattering by optical phonons at q similar to 0 (for x approximate to 0) and the density of vibrational states for x>0.1. Raman spectra from the undoped LaMnO3 structure distorted by the static Jahn-Teller effect are consistent with the orthorhombic D-2h(16), space group. Raman spectra of the doped La1-xMxMnO3 crystals have weakly resolved features and intensities comparable to those of the second-order spectra in cubic media. The anomalies in the phonon spectra of doped crystals were explained by the doping dependence of the ionic radius of a La/Sr site. The most intense B-1g mode in LaMnO3 crystal has an abrupt frequency shift near T-N = 140 K, which corresponds to a paramagnetic to canted-antiferromagnetic phase transition. [S0163-1829(98)06725-3].