The Raman spectra of epitaxial thin films of ${\mathrm{La}}_2\mathrm{Co}\mathrm{Mn}{\mathrm{O}}_6$ on (001)-oriented $\mathrm{Sr}\mathrm{Ti}{\mathrm{O}}_3$ substrates have been measured in several exact scattering configuration between 12 and $890\mathrm{K}$. The polarization dependence of the spectra provide clear evidence for ordered $P{12}_1∕n1$ structure, differing from its parent $Fm\overline{3}m$ structure by the presence of rotational distortions. The correlation between the phonon modes in $Fm\overline{3}m$, $R\overline{3}$, and $P{12}_1∕n1$ 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 $P{12}_1∕n1–R\overline{3}$ transition up to $800\mathrm{K}$.

• Received 12 December 2006

DOI:https://doi.org/10.1103/PhysRevB.75.104118