Spin-phonon coupling and isotope-related pseudo-molecule vibrations in layered Cr$_2$Ge$_2$Te$_6$ ferromagnet
Grzegorz Krasucki, Katarzyna Olkowska-Pucko, Tomasz Woźniak, Mihai I. Sturza, Holger Kohlmann, Adam Babiński, Maciej R. Molas
Published: 2025/10/2
Abstract
The vibrational structure of chromium germanium telluride (Cr$_2$Ge$_2$Te$_6$, CGT) is investigated and a strong spin-phonon coupling is revealed. The measured high-resolution Raman scattering (RS) spectra are composed of the 10 Raman-active modes: 5A$_\textrm{g}$ and 5E$_\textrm{g}$, predicted by calculation using the density functional theory and identified using polarization-resolved RS measurements. We also studied the effect of temperature on the RS spectra of CGT from 5~K to 300~K. A strong magneto-phonon coupling in CGT is revealed at temperatures of about 150~K and 60~K, which are associated with the appearance of the local magnetic order in the material and the transition to the complete ferromagnetic phase, respectively. Moreover, a unique shape of the A$_g^5$ mode composed of a set of very narrow Raman peaks is simulated using a model that takes into account vibrations of Ge-Ge pseudo-molecules for various Ge isotopes.