# Temperature-dependent phonon spectra of magnetic random solid solutions

## TL;DR

This paper introduces a first-principles method to compute phonon spectra in magnetic random solid solutions, accounting for thermal magnetic fluctuations, and explains unusual phonon hardening observed experimentally in Fe-Pd and Fe-Pt alloys.

## Contribution

It develops a novel computational approach that incorporates magnetic and chemical disorder effects on phonons, explaining temperature-dependent phonon behavior in magnetic alloys.

## Key findings

- Accurately predicts phonon hardening in Fe-Pd and Fe-Pt alloys with temperature.
- Shows thermal magnetic fluctuations cause unusual phonon behavior.
- Provides insights into phonon-magnetic interactions in disordered alloys.

## Abstract

A first-principles-based method for computing phonons of magnetic random solid solutions including thermal magnetic fluctuations is developed. The method takes fluctuations of force constants (FCs) due to magnetic excitations as well as due to chemical disorder into account. The developed approach correctly predicts the experimentally observed unusual phonon hardening of a transverse acoustic mode in Fe-Pd an Fe-Pt Invar alloys with increasing temperature. This peculiar behavior, which cannot be explained within a conventional, harmonic picture, turns out to be a consequence of thermal magnetic fluctuations.