# Lattice dynamics and phase transitions in Fe$_{3-x}$GeTe$_2$

## TL;DR

This study investigates the lattice vibrations and phase transitions in Fe$_{3-x}$GeTe$_2$ using Raman spectroscopy, revealing unusual temperature-dependent behaviors linked to magnetic transitions and other anomalies.

## Contribution

The paper combines experimental Raman measurements with numerical calculations to identify vibrational modes and analyze their temperature dependence in Fe$_{3-x}$GeTe$_2$.

## Key findings

- Observation of four Raman active modes consistent with calculations
- Unconventional temperature dependence of mode energies and linewidths around 150 K and 220 K
- Detection of nonmonotonic evolution of Raman continuum

## Abstract

We present Raman spectroscopy measurements of the van der Waals bonded ferromagnet Fe$_{3-x}$GeTe$_2$, together with lattice dynamics. Four out of eight Raman active modes are observed and assigned, in agreement with numerical calculations. The energies and line-widths of the observed modes display an unconventional temperature dependence at about 150 K and 220 K, followed by the nonmonotonic evolution of the Raman continuum. Whereas the former can be related to the magnetic phase transition, the origin of the latter anomaly remains an open question.