Effect of magnetism on lattice dynamics in SrFe$_2$As$_2$ as seen via high resolution inelastic x-ray scattering

TL;DR

This study investigates how magnetism influences lattice vibrations in SrFe$_2$As$_2$ using high-resolution inelastic x-ray scattering, revealing anisotropic phonon behavior linked to magnetic transitions and fluctuations.

Contribution

The paper introduces a magnetic DFT model incorporating magnetic fluctuations to explain phonon mode splitting and linewidths in SrFe$_2$As$_2$, providing insights into phonon-magnetism interactions.

Findings

Phonon spectra show anisotropy across the magnetic transition.

Magnetic fluctuations affect phonon mode splitting.

Lower bound on magnetic fluctuation frequency above T_N established.

Abstract

Phonon spectra of detwinned {SrFe$_2$As$_2$} crystals, as measured by inelastic x-ray scattering, show clear anisotropy accompanying the magneto-structural transition at 200 K. We model the mode splitting using magnetic DFT calculations, including a phenomenological reduction in force-constant anisotropy that can be attributed to magnetic fluctuations. This serves as a starting point for a general model of phonons in this material applicable to both magnetic and non-magnetic phase. Using this model, the measured splitting in the magnetic phase below $\it T_{N}$, and the measured phonon linewidth, we set a lower bound on the mean magnetic fluctuation frequency above $\it T_{N}$ at 210 K.