Raman spectroscopy ofRuSr2GdCu2O8thin films

Abstract

Polarization-resolved Raman data are reported for c-axis oriented thin films of ${\mathrm{RuSr}}_{2}{\mathrm{GdCu}}_{2}{\mathrm{O}}_{8}$ (Ru1212). The spectra show the same lines as were seen in polycrystalline ceramic material, although their relative intensities differ. A comparison of the film with polycrystalline spectra establishes that the strongest line at $650 {\mathrm{cm}}^{\ensuremath{-}1}$ shows a substantially reduced intensity in $\mathrm{ab}$ as compared to c-axis polarizations, which confirms the O(Sr) phonon assignment for the line. The line at $320 {\mathrm{cm}}^{\ensuremath{-}1},$ previously assigned as a ${B}_{1g}$-like O(Cu) mode, is seen particularly strongly in crossed polarizations, confirming its assignment as well. Finally, we observe spin-ordering-dependent features which are compared with similar phenomena reported earlier for the sintered material. As a function of decreasing temperature a line develops below the magnetic ordering temperature ${(T}_{M})$ and shifts up to $\ensuremath{\sim}130 {\mathrm{cm}}^{\ensuremath{-}1}.$ An ${A}_{1g}$ symmetry phonon line observed at $\ensuremath{\sim}260 {\mathrm{cm}}^{\ensuremath{-}1},$ and which we assign to O(Ru) vibrations, hardens strongly below ${T}_{M}.$ This latter peak, and the $\ensuremath{\sim}130 {\mathrm{cm}}^{\ensuremath{-}1}$ line, are substantially broader than in polycrystalline Ru1212. In addition, a diffusivelike laser tail characteristic of overdamped excitations (and which in retrospect is also weakly visible in polycrystalline Ru1212), is observed to disappear with decreasing temperature.