Correlation between magnetism and lattice dynamics for cubic FeGe under pressure

TL;DR

This study uses first-principles calculations to explore how pressure affects magnetism, lattice vibrations, and electron-phonon interactions in cubic FeGe, revealing a close link between magnetic moment reduction and phonon behavior.

Contribution

It introduces a spin-scaling exchange-correlation approach to accurately model pressure effects on magnetic and lattice properties in FeGe, aligning theoretical results with experimental observations.

Findings

Magnetic moment decreases with pressure, matching experimental data.

Phonon softening and linewidths diminish as pressure approaches critical value.

Electron-phonon matrix elements correlate with phonon linewidths and magnetic moment changes.

Abstract

This first-principles study investigates the structural, electronic, lattice dynamical properties, and electron-phonon coupling in ferromagnetic cubic B20 FeGe under applied pressure. The implemented spin-scaling exchange-correlation (ssxc) approach allowed to modify the magnetic moment and ferromagnetic phase energetics using a single scaling parameter, thereby yielding an adjustment of the critical pressure ($p_c$) to its experimental value. The ssxc scheme resulted in a subtle energy shift of the electronic bands in the spin-up channel, and reduced the magnetic moment, bringing it closer to the experimentally reported value. Application of the ssxc approach to phonon dispersion and electron-phonon interaction resulted in a slight mitigation of the pronounced softening and large linewidths of the lowest-frequency acoustic branch close to the $R$-point, typically observed with standard DFT calculations. With increasing pressure, phonon anomaly and linewidths diminish significantly and practically disappear at $p_c$ and beyond. This trend parallels the pressure dependence of the magnetic moment. A comparative analysis of the electronic joint density of states with the phonon linewidths revealed that the momentum dependence of linewidths around the $R$-point closely follow the momentum dependence of the electron-phonon matrix elements. This indicates that the correlation between magnetic moment and linewidths under applied pressure originates from the electron-phonon matrix elements, presenting a distinct scenario compared to other B20 family members, where nesting plays a more dominating role.