Journal
PRAMANA-JOURNAL OF PHYSICS
Volume 74, Issue 2, Pages 281-291Publisher
INDIAN ACAD SCIENCES
DOI: 10.1007/s12043-010-0027-6
Keywords
Spin-phonon coupling; longitudinal and transverse optic modes; effective charge; energy loss function
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Funding
- Department of Science and Technology (DST), India
- Council of Scientific and Industrial Research (CSIR), India
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We have measured near normal incidence far-infrared (FIR) reflectivity spectra of a single crystal of TbMnO3 from 10 K to 300 K in the spectral range of 50 cm(-1)-700 cm(-1). Fifteen transverse optic (TO) and longitudinal optic (LO) modes are identified in the imaginary part of the dielectric function epsilon(2)(omega) and energy loss function Im(-1/epsilon(omega)), respectively. Some of the observed phonon modes show anomalous softening below the magnetic transition temperature T-N (similar to 46 K). We attribute this anomalous softening to the spin-phonon coupling caused by phonon modulation of the superexchange integral between the Mn3+ spins. The effective charge of oxygen (Z(O)) calculated using the measured LO-TO splitting increases below TN.
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