# Vibrational properties and stability of FePt nanoalloys

## TL;DR

This study uses density functional theory to analyze how size, shape, and composition affect the vibrational stability of FePt nanoparticles, revealing structural distortions, vibrational anisotropy, and stability conditions.

## Contribution

It provides new insights into the vibrational properties and stability mechanisms of FePt nanoalloys with different geometries and compositions.

## Key findings

- Cuboctahedral FePt nanoparticles show structural distortions with odd Pt layers.
- Icosahedral particles are unstable unless modified by removing or replacing the central atom.
- Nanoparticles exhibit enhanced heat capacity and entropy due to surface low-energy vibrations.

## Abstract

The structural and dynamical properties of FePt nanoparticles were studied within the density functional theory. The effect of size and chemical composition on dynamical stability of nanoparticles was investigated for the cuboctahedral and icosahedral symmetries. In cuboctahedra, the structural distortion is observed, which for systems with odd number of Pt layers leads to lowering of the tetragonal symmetry. Significant differences between the vibrational properties of FePt particles and bulk crystal is observed, but similarly to the FePt crystal, cuboctahedral particles exhibit a strong anisotropy of atomic vibrations. The icosahedral particles with perfect shell geometry are unstable due to enlarged distances between Fe atoms. They can be stabilized by removing a central atom or replacing it by a smaller one. The heat capacity and entropy of nanoparticles show typical enhancement due to low-energy vibrations at the surface layers.