Phonons as a probe of the magnetic state in doped and undoped BaFe2As2

TL;DR

This study investigates how phonon properties in BaFe2As2 relate to its magnetic state, revealing that phonons are more sensitive to magnetic fluctuations than static magnetic order, with implications for understanding magnetic interactions in this material.

Contribution

The paper demonstrates that phonons in BaFe2As2 are coupled to high-frequency magnetic fluctuations rather than static magnetic order, supported by experimental and theoretical comparisons.

Findings

Phonon frequencies align better with magnetic DFT calculations.

Phonon frequencies are unaffected by doping or temperature changes.

No peak splitting due to magnetic domain twinning was observed.

Abstract

We measured phonon frequencies and linewidths in doped and undoped BaFe2As2 single crystals by inelastic x-ray scattering and compared our results with density functional theory (DFT) calculations. In agreement with previous work, the calculated frequencies of some phonons depended on whether the ground state was magnetic or not and, in the former case, whether phonon wavevector was parallel or perpendicular to the magnetic ordering wavevector. The experimental results agreed better with the magnetic calculation than with zero Fe moment calculations, except the peak splitting expected due to magnetic domain twinning was not observed. Furthermore, phonon frequencies were unaffected by the breakdown of the magnetic ground state due to either doping or increased temperature. Based on these results we propose that phonons strongly couple not to the static order, but to high frequency magnetic fluctuations.