Tuning the magnetic interactions in van der Waals Fe3GeTe2 heterostructures: A comparative study of ab initio methods

Abstract

We investigate the impact of mechanical strain, stacking order, and external electric fields on the magnetic interactions of a two-dimensional (2D) van der Waals heterostructure in which a 2D ferromagnetic metallic Fe 3 GeTe 2 monolayer is deposited on germanene. Three distinct computational approaches based on ab initio methods are used, (i) the Green's function method, (ii) the generalized Bloch theorem, and (iii) the supercell approach, and a careful comparison is given. First, the shell-resolved exchange constants are calculated for the three Fe atoms within the unit cell of the freestanding Fe 3 GeTe 2 monolayer. We find that the results obtained with approaches (i) and (ii) are in good qualitative agreement and also in good qualitative agreement with previously reported values. An electric field of E = ±0.5 V/Å applied perpendicular to the Fe 3 GeTe 2 /germanene heterostructure leads to significant changes in the exchange constants. We show that the Dzyaloshinskii-Moriya interaction (DMI) in Fe 3 GeTe 2 /germanene is mainly dominated by the nearest neighbors, resulting in a good quantitative agreement between approaches (i) and (ii). Furthermore, we demonstrate that the DMI is highly tunable by strain, stacking, and electric field, leading to a large DMI comparable to that of ferromagnetic/heavy metal interfaces, which have been recognized as prototypical multilayer systems to host isolated skyrmions. The geometrical change and hybridization effect explain the origin of the high tunability of the DMI at the interface. The electric-field-driven DMI obtained by approach (iii) is in qualitative agreement with the more accurate ab initio method used in approach (ii). However, the field effect on the DMI is overestimated by approach (iii) by about 50%. This discrepancy is attributed to the different implementations of the electric field and basis sets used in the ab initio methods applied in approaches (ii) and (iii). The magnetocrystalline anisotropy energy (MAE) can also be drastically changed by the application of compressive or tensile strain in the Fe 3 GeTe 2 /germanene heterostructure. The application of an electric field, in contrast, leads only to relatively small changes in the MAE for electric fields of up to 1 V/Å.

Proposal for All-Electrical Skyrmion Detection in van der Waals Tunnel Junctions

“…We consider FGT/Ge (Figure a) as a representative 2D vdW magnet heterostructure and a skyrmion platform for several reasons. First, there is strong experimental evidence of magnetic skyrmions in vdW FGT heterostructures. − Second, FGT has a very high Curie temperature, which can vary from 150 to 220 K depending on the Fe occupancy. , Third, recent theoretical work based on first-principles calculations and atomistic spin simulations predicts that magnetic interactions in FGT/Ge cane be strongly tuned with strain, leading to the stabilization of nanoscale skyrmions with diameters down to a few nanometers . Finally, the properties of atomically thin vdW layers can be controlled by external stimuli, which makes them ideal skyrmion platforms from the perspective of materials design.…”

On the Origin of the Above-Room-Temperature Magnetism in the 2D van der Waals Ferromagnet Fe3GaTe2

“…However, more significant differences appear upon examination of the in-plane exchanges. In Fe 3 GeTe 2 , the J 11 and J 33 interactions are antiferromagnetic (AF), resulting in a geometrically frustrated spin–lattice. − Conversely, for Fe 3 GaTe 2 , J 11 and J 33 display values of 1.1 and −0.04 meV, respectively, indicating that the AF contribution of the in-plane couplings is almost suppressed, which, in turn, amplifies the net ferromagnetism. In Supporting Information Section 1.3, we show a comparison of the exchange parameters of Fe 3 GaTe 2 with those in the existing bibliography, employing a common notation.…”