Raman scattering study of anomalous charge-, spin-, and lattice-dynamics in the charge-ordered phase of ${\bf Bi}_{1-x}{\bf Ca}_x{\bf MnO}_3$ ($x>0.5$)

Abstract

We report an inelastic light scattering study of the effects of charge-ordering on the spin-, charge-, and lattice-dynamics in ${\rm Bi}_{1-x}{\rm Ca}_{x}{\rm MnO}_3$ $(x>0.5)$. We find that charge-ordering results in anomalous phonon behavior, such as the appearance of `activated' modes. More significantly, however, the transition to the CO phase results in the appearance of a quasielastic scattering response with the symmetry of the spin chirality operator ($T_{1g}$); this scattering response is thus indicative of magnetic or chiral spin fluctuations in the AFM charge-ordered phase.