Magnetic ordering effects in the Raman spectra ofLa1−xMn1−xO3

Abstract

Temperature-dependent Raman spectra of polycrystalline ${\mathrm{La}}_{1-x}{\mathrm{Mn}}_{1-x}{\mathrm{O}}_3$ samples, referred to as ${\mathrm{LaMnO}}_{3+\delta }$ for convenience, were correlated to their structural and magnetic properties for different $\delta .$ For $\delta <~0.05,$ a softening of the $\sim 610\hspace{0.5em}{\mathrm{cm}}^{-1}$ Raman mode is observed below the magnetic ordering temperature. This softening is reduced as $\delta$ increases from 0.00 to 0.05. This behavior is not associated with lattice anomalies, and is interpreted in terms of a spin-phonon coupling caused by a phonon modulation of the superexchange integral. A quantitative analysis of this effect is presented.