Magnetic critical behavior of the van der Waals Fe5GeTe2 crystal with near room temperature ferromagnetism

Abstract

The van der Waals ferromagnet Fe5GeTe2 has a Curie temperature TC of about 270 K, which is tunable through controlling the Fe deficiency content and can even reach above room temperature. To achieve insights into its ferromagnetic exchange that gives the high TC, the critical behavior has been investigated by measuring the magnetization in Fe5GeTe2 crystal around the ferromagnetic ordering temperature. The analysis of the measured magnetization by using various techniques harmonically reached to a set of reliable critical exponents with TC = 273.7 K, β = 0.3457 ± 0.001, γ = 1.40617 ± 0.003, and δ = 5.021 ± 0.001. By comparing these critical exponents with those predicted by various models, it seems that the magnetic properties of Fe5GeTe2 could be interpreted by a three-dimensional magnetic exchange with the exchange distance decaying as J(r) ≈ r−4.916, close to that of a three-dimensional Heisenberg model with long-range magnetic coupling.

Large-scale epitaxy of two-dimensional van der Waals room-temperature ferromagnet Fe5GeTe2

“…The Mr can be reasonably fitted with 3D models (see Supplementary Figure 4). However, our determined β significantly deviates from the corresponding magnetic critical exponent and from the one observed in bulk-crystals β ≈ 0.346 23 . With a value of β ≈ 0.294, our results approaches the window for critical exponents of two-dimensional systems 34 , and possibly indicates a characteristic 2D behavior in ultrathin films.…”

“…using Fe-deficient bulk crystals or micrometer-sized flakes exfoliated from them 7,[21][22][23] . The properties of Fe5GeTe2 films with exact 5:1:2 stoichiometry remain unexplored.…”

“…Recent studies pointed out the role played by Fe vacancies and the different Fe sublattices on the complex range of magnetic behaviors observed 6,7,21 . Additionally, magnetic critical exponents of bulk Fe5-δGeTe2 are close to those of a 3D Heisenberg and 3D XY systems 23 , remaining unclear if these models still hold in ultrathin regimes.…”

Magnetism and Spin Dynamics in Room-Temperature van der Waals Magnet Fe$_5$GeTe$_2$

“…For example, T c can be significantly raised to about room temperature by enhancing exchange interaction while keeping the vdWs structure, 12 such as in the layered 2D Fe n GeTe 2 (n≥ 3). 13,14 This led to Fe 3 GeTe 2 with T c around 220 K, 9,15,16 Fe 4 GeTe 2 with T c = 270 K, 12 and Fe 5 GeTe 2 with T c ranging from 260 -310K, depending on the Fe content. 14,17,18 Ferromagnetic resonance (FMR) spectroscopy is an important technique to study magnetization dynamics.…”

“…13,14 This led to Fe 3 GeTe 2 with T c around 220 K, 9,15,16 Fe 4 GeTe 2 with T c = 270 K, 12 and Fe 5 GeTe 2 with T c ranging from 260 -310K, depending on the Fe content. 14,17,18 Ferromagnetic resonance (FMR) spectroscopy is an important technique to study magnetization dynamics. 19,20 Several studies have analyzed the spin dynamics in 2D magnets by FMR, [21][22][23] which revealed their magnetocrystalline anisotropy dependence on temperature.…”