Raman spectroscopy of the charge- and orbital-ordered state in La{sub 0.5}Ca{sub 0.5}MnO{sub 3}

Journal Article · Mon Oct 01 04:00:00 EDT 2001 · Physical Review B

DOI:https://doi.org/10.1103/PhysRevB.64.144429· OSTI ID:40277682

Abrashev, M V; Baeckstroem, J; Boerjesson, L; Pissas, M; Kolev, N; Iliev, M N

Polarized Raman spectra from microcrystals of La{sub 0.5}Ca{sub 0.5}MnO{sub 3} were studied as a function of temperature, excitation photon energy, and scattering configuration. At temperatures below the transition from ferromagnetic metallic phase to antiferromagnetic insulating charge- and orbital-ordered (COO) phase, several lines appear in Raman spectra excited with photon energies {Dirac_h}{omega}{sub L}<2.5 eV. We argue that their appearance signals ordering and freezing of the Jahn-Teller distortions at this transition temperature into a superstructure with a doubled elementary cell. We suggest a simplified structural model based on an analysis of the normal phonon modes in the COO phase, neglecting the octahedral tilts and containing ordered Mn{sup 4+}O{sub 6} (undistorted) and Mn{sup 3+}O{sub 6} (Jahn-Teller distorted) octahedra. The symmetries of the experimentally observed Raman lines are determined by comparing their relative intensities to those predicted by the polarization selection rules for a finely twinned quasicubic crystal. The most intensive Raman lines are assigned to definite normal modes in close comparison with corresponding modes in COO layered manganites and undoped RMnO{sub 3} (R=La, Y).

• Sponsoring Organization: (US)
• OSTI ID: 40277682
• Journal Information: Physical Review B, Journal Name: Physical Review B Journal Issue: 14 Vol. 64; ISSN 0163-1829
• Publisher: The American Physical Society
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
CONFIGURATION
EXCITATION
FREEZING
PHONONS
PHOTONS
POLARIZATION
RAMAN SPECTRA
RAMAN SPECTROSCOPY
SCATTERING
SELECTION RULES
STRUCTURAL MODELS
TRANSITION TEMPERATURE