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The polarized Raman spectra of orthorhombic RMnO3 series (R=La,Pr,Nd,Sm,Eu,Gd,Tb,Dy,Ho,Y) were studied at room temperature.The variation of phonon frequencies with R ionic radius rR as a whole confirms the commonly accepted Raman line assignments with two noticeable exceptions: (1) with decreasing rR the stretching Ag(1) and bending Ag(3) modes strongly mix for R=Sm to Tb, while for further decrease or rR (R=Dy,Ho,Y) the Ag(3) mode is observed at higher frequency than Ag(1) mode; (2) similar distortion-dependent mode mixing takes place for the rotational Ag(2) and O1(x) [Ag( 7)] modes. The mode mixing is particularly strong for the RMnO3 compounds with rR values close to the transition from A-type to incommensurate sinusoidal antiferromagnetic ordering at low temperatures. The frequency of rotational Ag(2) and Ag(4) modes scales to the angles of MnO6 [101] and [010] rotations, respectively, and could be used as a measure of their value.

The Raman spectra of epitaxial thin films of La 2 CoMnO 6 on ͑001͒-oriented SrTiO 3 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 Fm3m structure by the presence of rotational distortions. The correlation between the phonon modes in Fm3m, R3, 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-R3 transition up to 800 K.

The Raman spectra of epitaxial thin films of La2NiMnO6 on (001)-oriented LaAlO3 substrates have been measured in several exact scattering configurations between 12 and 773K. The evolution of the spectra with increasing temperature is consistent with a transition from the monoclinic P121∕n1 to rhombohedral R3¯ structure. The spin-phonon coupling results in significant softening of the phonon mode involving stretching vibrations of the (Ni∕Mn)O6 octahedra. The anomalous softening extends above TC=275K, indicating the presence of short range ordering up to 400K.

We have investigated the nanoscale switching properties of strain-engineered BiFeO 3 thin films deposited on LaAlO 3 substrates using a combination of scanning probe techniques. Polarized Raman spectral analysis indicate that the nearly-tetragonal films have monoclinic (Cc) rather than P4mm tetragonal symmetry. Through local switching-spectroscopy measurements and piezoresponse force microscopy we provide clear evidence of ferroelectric switching of the tetragonal phase but the polarization direction, and therefore its switching, deviates strongly from the expected (001) tetragonal axis. We also demonstrate a large and reversible, electrically-driven structural phase transition from the tetragonal to the rhombohedral polymorph in this material which is promising for a plethora of applications.