Abstract
The polarized Raman spectra of La0.7Ca0.3MnO3 magnetoresistive thin films deposited on LaAlO3, SrTiO3, YSZ, and MgO substrates were studied in a broad temperature range including Tc. Depending on variations of their intensity and linewidth upon cooling, the Raman bands could be classified into two groups. The lines corresponding to Raman allowed modes of the rhombohedral (or orthorhombic) structure grow in intensity and become narrower at low temperatures. In contrast, the broad Raman bands centered near 470, 485 and 610 cm—1 strongly decrease in intensity below Tc and display a correlation to the resistivity of the sample. We argue that these bands correspond to lattice vibrations activated by the dynamic Jahn-Teller distortions and by presence of small polarons around the Mn3+ sites. The correlation between polaron lifetimes and phonon linewidth is also discussed.
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