Lattice dynamics and phase transitions in Fe3−xGeTe2

Abstract

We present Raman spectroscopy measurements of van der Waals bonded ferromagnet Fe3−xGeTe2, together with lattice dynamics. Four out of eight Raman active modes are observed and assigned, in agreement with numerical calculations. Energies and line-widths of the observed modes display unconventional temperature dependence at about 150 K and 220 K followed by the non-monotonic evolution of the Raman continuum. Whereas the former can be related to the magnetic phase transition, origin of the latter anomaly remains an open question.

Thickness and Spin Dependence of Raman Modes in Magnetic Layered Fe3GeTe2

“…194), which corresponds to point group. [ 24,25 ] Because the unit cell of the bulk has 12 atoms in total, it possesses 36 phonon normal modes at the Γ point, which can be decomposed as Raman active modes correspond to non‐degenerate A 1 g , twofold degenerate E 1 g , and twofold degenerate E 2 g . Their Raman tensors are shown in Table 1, as determined by group theory.…”

“…Since most of experimentally observed Raman peaks in Fe 3 GeTe 2 reside above 100 cm −1 , [ 24,25 ] our study is focused on Raman modes above 100 cm −1 , where there are two A 1 g modes and three pairs of E 2 g modes, as shown in Table 2 . The calculated atomic displacement patterns of these five Raman modes are illustrated in Figure .…”

“…At present, there are limited studies on the lattice dynamics in Fe 3 GeTe 2 , [ 24,25 ] where the focus was on the bulk and thick samples with only the interlayer FM order considered. In this work, we carry out a systematic computational study of the lattice dynamics in the bulk, bilayer and monolayer Fe 3 GeTe 2 with both interlayer FM and AFM orderings taken into account, so we can reveal the delicate effects of the layer number and interlayer spin ordering on the Raman modes.…”

Probing the Ferromagnetism and Spin Wave Gap in VI3 by Helicity-Resolved Raman Spectroscopy

“…In the study of 2D magnets, the Raman spectrum of optical phonons has been widely used to study the magnetic phase transition through some indirect phenomena, such as spin–phonon coupling, , the structural phase transition, and Brillouin zone folding. − Recently, the discovery of the magneto-optic Raman effect in CrI 3 proved that the magnetic order could greatly affect the Raman scattering of phonons, , which implies that Raman spectroscopy could be used to probe the magnetic phase transition directly through the polarization properties of phonon scattering. Furthermore, Raman spectroscopy can also be used to detect the spin wave excitations, especially the acoustic magnon (the spin wave gap) which resulted from the magnetic anisotropy which brings stability to the long-range magnetic order in the 2D limit.…”

Vacancies and spin–phonon coupling in CrSi0.8Ge0.1Te3

“…Namely, in the recent years, large family of van der Waals materials with inherent magnetism became the focus of experimental and theoretical research, because they seem suitable for numerous technical applications. [ 1‐7 ] The family includes Fe 3 − x GeTe 2 metallic materials with high magnetic transition temperature, [ 8‐10 ] semiconductors CrXTe 3 (X = Si, Ge, Sn) and CrX 3 (X = Cl, Br, I) monolayers [ 2,11‐13 ] and heterostructures. [ 14 ]…”