Magnetic Moments and Vibrations: Unraveling the Pressure-Induced Dance in FeGe

Scientists have delved into the intriguing behavior of ferromagnetic (FM) cubic B20 FeGe, specifically how its structural, electronic, and vibrational properties, along with electron-phonon coupling, respond to applied pressure. The investigation utilized a sophisticated first-principles approach, focusing on understanding the interplay between magnetism and the material's atomic vibrations.

A key innovation in this study was the implementation of a spin-scaling exchange-correlation (ssxc) method. This technique allowed researchers to precisely modify the material's magnetic moment and the energetics of its FM phase using a single scaling parameter. This adjustment proved crucial for aligning the calculated critical pressure (pc) to its experimental value. The ssxc scheme not only subtly shifted the energy of electronic bands in the spin-up channel but also refined the magnetic moment, bringing theoretical predictions closer to experimentally reported values.

Applying the ssxc approach to the phonon dispersion and electron-phonon interaction yielded significant insights. It successfully mitigated the pronounced softening and large linewidths typically observed in the lowest-frequency acoustic branch close to the R-point in standard density functional theory calculations. As pressure increased, these phonon anomalies and linewidths diminished significantly and practically disappeared at pc and beyond. This trend mirrored the pressure dependence of the magnetic moment, suggesting a deep connection.

A detailed comparison of the electronic joint density of states with phonon linewidths illuminated the underlying mechanism. The study found that the momentum dependence of linewidths around the R-point closely tracked the momentum dependence of the electron-phonon matrix elements. As lead author Tonacatl-Monez notes in the paper, "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."