Determinative Role of the Jahn-Teller Disorder in the Raman Scattering of Mixed-Valence Manganites

TL;DR

This paper investigates how Jahn-Teller disorder influences Raman scattering in mixed-valence manganites, revealing that disorder-induced phonon density of states dominates the Raman spectra in insulating phases.

Contribution

It demonstrates the dominant role of Jahn-Teller disorder in shaping Raman spectra and links spectral features to oxygen partial phonon density of states in mixed-valence manganites.

Findings

Raman spectra are dominated by disorder-induced bands in insulating phases.

Main Raman bands originate from oxygen partial phonon density of states.

Ordered ferromagnetic metallic phases lack these disorder-induced bands.

Abstract

The mixed-valence perovskitelike manganites are characterized by unique interrelation of Jahn-Teller distortions, electric and magnetic properties. The Jahn-Teller distortion follows the Mn(3+)->Mn(4+) charge transfer with some delay. Its development depends on the lifetime of Mn in (3+) state, governed by the Mn(4+)/Mn(3+) ratio and magnetic correlation. The non-coherence of Jahn-Teller distortions in orthorhombic mixed-valence manganites and rhombohedral RMnO3 (R = rare earth) results in oxygen disorder. We demonstrate that the Raman spectra in this case are dominated by disorder-induced bands reflecting the oxygen partial phonon density of states (PDOS). The PDOS origin of the main Raman bands in insulating phases of such compounds is evidenced by the similar lineshape of experimental spectra and calculated smeared PDOS and disappearance of the PDOS bands in ordered ferromagnetic metallic phase.