Lattice dynamics in the double-helix antiferromagnet FeP

TL;DR

This study combines neutron spectroscopy and ab-initio calculations to analyze lattice vibrations in FeP, revealing detailed phonon spectra and their agreement with DFT predictions, with some discrepancies at specific points.

Contribution

It provides a comprehensive experimental and theoretical analysis of phonons in FeP, demonstrating DFT's effectiveness and identifying specific modes with deviations.

Findings

Phonons extend up to ~50 meV with rich spectra.

DFT accurately predicts phonon dispersions and intensities.

Discrepancy observed at the lowest mode at the Y-point, lower than calculations by ~13%.

Abstract

We present a comprehensive investigation of lattice dynamics in the double-helix antiferromagnet FeP by means of high-resolution time-of-flight neutron spectroscopy and ab-initio calculations. Phonons can hybridize with the magnetic excitations in noncollinear magnets to significantly influence their properties. We observed a rich spectrum of phonon excitations, which extends up to $\sim$50 meV. We performed detailed analysis of the observed and calculated spectra for all high-symmetry points and high-symmetry directions of the Brillouin zone. We show that the DFT calculations quantitatively capture the essential features of the observed phonons, including both dispersions and scattering intensities. By making use of the detailed intensity comparison between the theory and the data, we were able to identify displacement vectors for the majority of the observed modes. The overall excellent agreement between the DFT predictions and the experimental results breaks down for the lowest mode at the $Y$-point, whose energy is lower than calculated by $\sim$13%. The present study provides vital information on the lattice dynamics in FeP and demonstrates applicability of the DFT to novel pressure-induced phenomena in related materials, such as MnP and CrAs.