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 crysta ls have been studied in the temperature range from 5 to 423 K (M=Sr, C a). 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 st ructure distorted by the static Jahn-Teller effect are consistent with the orthorhombic D-2h(16), space group. Raman spectra of the doped La 1-xMxMnO3 crystals have weakly resolved features and intensities compa rable to those of the second-order spectra in cubic media. The anomali es in the phonon spectra of doped crystals were explained by the dopin g dependence of the ionic radius of a La/Sr site. The most intense B-1 g mode in LaMnO3 crystal has an abrupt frequency shift near T-N = 140 K, which corresponds to a paramagnetic to canted-antiferromagnetic pha se transition. [S0163-1829(98)06725-3].