Dynamical properties of ordered Fe-Pt alloys

TL;DR

This study combines density functional theory calculations with experimental measurements to explore the structural, magnetic, and lattice dynamical properties of ordered Fe-Pt alloys, revealing insights into phase transformations and magnetic effects.

Contribution

It provides a comprehensive analysis of Fe-Pt alloys' phonon spectra and magnetic properties, including new experimental data and comparison with theoretical models.

Findings

Phonon dispersion relations match well with calculations.

Softening of the TA1 mode indicates tetragonal phase relevance.

Weak dependence of phonon density of states on magnetic order.

Abstract

The structure, magnetic properties, and lattice dynamics of ordered Fe-Pt alloys with three stoichiometric compositions, Fe$_3$Pt, FePt and FePt$_3$, have been investigated using the density functional theory. Additionally, the existing experimental data have been complemented by new measurements of the Fe projected phonon density of states performed for the Fe$_3$Pt and FePt$_3$ thin films using the nuclear inelastic scattering technique. The calculated phonon dispersion relations and phonon density of states have been compared with the experimental data. The dispersion curves are very well reproduced by the calculations, although, the softening of the transversal acoustic mode TA$_1$ leads to some discrepancy between the theory and experiment in Fe$_3$Pt. A very goood agreement between the measured spectra and calculations performed for the tetragonal structure derived from the soft mode may signal that the tetragonal phase with the space group $P4/mbm$ plays an important role in the martensitic transformation observed in Fe$_3$Pt. For FePt$_3$, the antiferromagnetic order appearing with decreasing temperature has been also investigated. The studies showed that the phonon density of states of FePt$_3$ very weakly depends on the magnetic configuration.