Raman spectroscopy of ordered double perovskite La2CoMnO6 thin films

The Raman spectra of epitaxial thin films of La2CoMnO6 on (001)-oriented SrTiO3 substrates have been measured in several exact scattering configuration between 12 and 890 K. The polarization dependence of the spectra provide clear evidence for ordered P12(1)/n1 structure, differing from its parent Fm (3) over barm structure by the presence of rotational distortions. The correlation between the phonon modes in Fm <(3)over bar > m, R, and P12(1)/n1 phases is analyzed and the corresponding types of atomic motions as well as their expected frequency range are determined by comparison to the predictions of lattice dynamical calculations. The ferromagnetic ordering and spin-phonon coupling below T-C result in softening of some of the phonon modes. The evolution of the Raman spectra at high temperatures shows no indication for P12(1)/n1-R (3) over bar transition up to 800 K.