Abstract
We combined spectroscopic ellipsometry, Raman scattering spectroscopy, and first-principles calculations to explore the optical properties of YBaCuFeO5 single crystals. Measuring the optical absorption spectrum of YBaCuFeO5 at room temperature revealed a direct optical band gap at approximately 1.41 eV and five bands near 1.69, 2.47, 3.16, 4.26, and 5.54 eV. Based on first-principles calculations, the observed optical excitations were appropriately assigned. Analysis of the temperature dependence of the band gap indicated anomalies in antiferromagnetic phase transition at 455 and 175 K. Additionally, a hardening in the frequency of the Eg phonon mode was observed at 175 K. The value of the spin–phonon coupling constant was 15.7 mRy/Å2. These results suggest a complex nature of spin–charge–lattice interactions in YBaCuFeO5.
Highlights
We examined the correlation of the optical response with the magnetic phase transitions of YBaCuFeO5
To investigate the electronic structure of YBaCuFeO5, we modeled several YBaCuFeO5 systems using density functional theory (DFT) calculations in the Vienna ab initio Simulation Package (VASP)[21,22]
Optical transitions were identifiable in the spectra based on resonance and antiresonance features, which appeared at the same energy in ε2 and ε1, respectively
Summary
A1g mode exhibited a slight deviation from the usual anharmonic contribution to the temperature dependence of the phonon frequency and linewidth through the 455 and 175 K antiferromagnetic ordering transitions. The frequency of the 579 cm−1 Eg mode deviated considerably from the theoretical predictions to below the antiferromagnetic phase transition temperature of 175 K. This effect was attributed to the renormalization of the in-plane Eg phonon induced by magnetic ordering, usually understood as a sign of Figure 7. The magnitude of this value was comparable to those obtained for other multiferroic manganites[44,45,46]
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