Lattice dynamics and structural stability of ordered Fe3Ni, Fe3Pd and Fe3Pt alloys

TL;DR

This study uses first-principles calculations to analyze lattice dynamics and stability of ordered Fe3X alloys, revealing phonon instabilities linked to atomic movements and Fermi surface changes, informing magnetic material design.

Contribution

It provides new insights into phonon behavior and structural stability of Fe3X alloys, highlighting the roles of electron density, Fe-content, and atomic masses.

Findings

Phonon softening at the M-point in Fe3Pt matches experimental data.

Instability involves Fe atom rotations and Fermi surface reconstruction.

Softening varies among Fe3Ni, Fe3Pd, and Fe3Pt, affecting stability.

Abstract

We investigate the binding surface along the Bain path and phonon dispersion relations for the cubic phase of the ferromagnetic binary alloys Fe3X (X = Ni, Pd, Pt) for L12 and DO22 ordered phases from first principles by means of density functional theory. The phonon dispersion relations exhibit a softening of the transverse acoustic mode at the M-point in the L12-phase in accordance with experiments for ordered Fe3Pt. This instability can be associated with a rotational movement of the Fe-atoms around the Ni-group element in the neighboring layers and is accompanied by an extensive reconstruction of the Fermi surface. In addition, we find an incomplete softening in [111] direction which is strongest for Fe3 Ni. We conclude that besides the valence electron density also the specific Fe-content and the masses of the alloying partners should be considered as parameters for the design of Fe-based functional magnetic materials.