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      https://www.ias.ac.in/article/fulltext/pram/074/02/0281-0291

    • Keywords

       

      Spin-phonon coupling; longitudinal and transverse optic modes; effective charge; energy loss function.

    • Abstract

       

      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 $\varepsilon_{2} (\omega)$ and energy loss function Im($−1/\varepsilon(\omega))$, respectively. Some of the observed phonon modes show anomalous softening below the magnetic transition temperature $T_{N}$ ($\sim 46$ 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 $T_{N}$.

    • Author Affiliations

       

      Pradeep Kumar1 Surajit Saha1 C R Serrao2 3 A K Sood1 3 C N R Rao3

      1. Department of Physics, Indian Institute of Science, Bangalore 560 012, India
      2. Material Research Centre, Indian Institute of Science, Bangalore 560 012, India
      3. Chemistry and Physics of Materials Unit and International Centre for Materials Science, Jawaharlal Nehru Centre for Advanced Scientific Research, Bangalore 560 064, India

    • Dates

       
      Published
      February 2010
      Manuscript received
      24 June 2009
      Manuscript revised
      12 September 2009
      Accepted
      15 September 2009

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