Effects of Fe Deficiency and Co Substitution in Polycrystalline and Single Crystals of Fe₃GeTe₂

Abstract

Fe3GeTe2 is a two-dimensional van der Waals material with a ferromagnetic ground state and a maximum transition temperature T c ∼ 225 K. However, when Fe3GeTe2 is synthesized, lower values of T c are often reported. This is attributed to a deficiency in the Fe at the 2c site in the crystal structure. Here, we investigate the effect of Fe deficiency and the substitution of Co for Fe on the magnetic properties of this system. We have synthesized both polycrystalline material and single crystals by chemical vapor transport and the flux method, with the largest crystals obtained using the flux method. Cobalt substitution at the Fe site is found to significantly reduce the magnetic transition temperature. Crystals of Fe3GeTe2 grown by chemical vapor transport with ∼ 8% excess Fe in the starting materials display an optimum Fe content and magnetic transition temperature.

Anisotropic laser-pulse-induced magnetization dynamics in van der Waals magnet Fe3GeTe2

“…A clear transition point corresponding to the Curie temperature T C = 191 ± 2 K is observed, with γ = 1.3 ± 0.1, which is close to the typical exponent for a three-dimensional Ising magnet (γ ∼ 1.25) [32]. We note that the Curie temperature is significantly lower than expected for stoichiometric FGT [21,[33][34][35][36], indicating that our material is slightly Fe deficient [37,38]. Following these works, we estimate that the region used for our experiments has an Fe deficiency of less than 7% (i.e.…”

Recent advances in two-dimensional intrinsic ferromagnetic materials Fe3X(X=Ge and Ga)Te2 and their heterostructures for spintronics

“…2a–d. 48,49 The unit cell of Fe 3 X ( X =Ge and Ga)Te 2 consists of one Fe 3 X ( X =Ge and Ga) layer and two adjacent Te layers, in which the Fe 3 X layer refer to Fe 2+ Ge 4− sandwiched by Fe 3+ atoms and the Ge and Fe 2 bonds covalently in Fe 3 GeTe 2 . 50 Different from those of Fe 3 GeTe 2 , the Fe valence states of Fe 3 GaTe 2 are Fe 0 and Fe 3+ were confirmed by X-ray photoelectron spectroscopy.…”

“…54 Mayoh et al also found the dependence of lattice constant on Fe concentrations and further revealed that both a and c decrease when Fe atoms are replaced by Co atoms in Fe 3− y Co y GeTe 2 . 49…”

“…77 Additionally, the TeCl 4 also can be used as transport agents. 49 Similar fabrication methods have also been utilized in other articles, 63,78,79 albeit with some variations in specific details. Regrettably, Nair et al 80 pointed out that owing to limited layer control and scalability in production, CVT constrains the potential applications of 2D materials.…”

“…For instance, Mayoh et al fabricated polycrystalline and monocrystalline Fe 3 GeTe 2 using the solid-state reaction method and CVT or self-flux method, respectively. 49 Additionally, CVT, 49 self-flux 49 and space-confined chemical vapor deposition 80 methods are used to fabricate Fe 3− y Co y GeTe 2 with different Fe concentrations. The fabrication method also exerts a pronounced influence on the properties of the materials.…”