Magnetic and Higher Order Lattice Excitations in LaFe(1-x)Cr(x)O(3) Perovskites

The resonance behavior of the oxygen breathing mode at 700 cm(- 1) and its higher orders is studied between 1.8 eV (676 nm) and 4.2 eV (300 nm) in the perovskite LaFe(0.5)Cr(0.5)O(3). The Franck-Condon induced higher order scattering present in the x=0.1, 0.5 and 0.9 compounds dominates the Raman spectrum in the visible energy region while a feature in the 1400 cm$^{-1}$ energy region dominates using UV lasers. The energy location of this peak coincides both with the second order Franck-Condon mode as well as similar feature seen in the x=0 and 1 compounds (and to some extent in the low doping compounds (x=0.02, 0.04, 0.06 and 0.08)) using the 2.41 eV ($\lambda $=514) laser, believed to be a two-magnon caused by a spin-flip excitation in the AFM spin-state. Thus the complex magnetism in the Fe/Cr perovskite is likely to be influenced by the competition between the magnetically ordered state and the lattice dynamics through the resonant Franck- Condon effect.