Fe3GeTe2: A 2D van der Waals Ferromagnet
- FGT is a layered, metallic van der Waals ferromagnet characterized by itinerant 3d magnetism, strong perpendicular anisotropy, and pronounced Berry curvature.
- Its crystal structure and thickness-dependent symmetry enable phenomena such as anomalous Hall transport, spin-current generation, and efficient spin–orbit torque switching.
- FGT’s tunability via pressure, interfacial engineering, and chemical intercalation makes it a versatile platform for exploring 2D magnetism and spintronic applications.
FeGeTe (FGT) is a layered, metallic van der Waals ferromagnet that combines itinerant $3d$ magnetism, strong perpendicular magnetic anisotropy, and pronounced Berry-curvature-driven transport. In bulk, few-layer, and monolayer forms, it has served as a model system for two-dimensional Ising ferromagnetism, anomalous Hall transport, spin-current generation, spin-orbit torque switching, exchange bias in all-van-der-Waals heterostructures, and field- or interface-stabilized domain textures including stripe domains and skyrmion bubbles (Fei et al., 2018, Alghamdi et al., 2019).
1. Crystal structure and electronic character
FGT is generally described as a hexagonal van der Waals material with space group , built from Fe–Ge–Te layers stacked along the crystallographic -axis and separated by weak van der Waals gaps. Across the cited literature, the layer-resolved description varies in emphasis: several studies describe Te–Fe–Ge–Fe–Te sandwich layers or Te–FeGe–Te triple layers, whereas one exchange-bias study describes Te–Fe–Ge–Fe–Fe–Ge–Fe–Te slabs stacked along . A monolayer step height of about $0.8$ nm is repeatedly reported, and the material can be mechanically exfoliated to the monolayer limit (Fei et al., 2018, Alghamdi et al., 2019, Tan et al., 2018, Wang et al., 2019, Cham et al., 2023).
FGT remains metallic in few-layer and monolayer-derived contexts, which distinguishes it from many insulating or semiconducting van der Waals magnets. First-principles calculations place Fe- bands at the Fermi level, hybridized with Te- states, and several works describe topological or nodal-line features accompanied by strong spin–orbit coupling and large Berry curvatures near 0. In monolayer FGT, the cited symmetry is 1, with threefold rotation, three vertical mirror planes, and a horizontal mirror 2; in bilayer FGT, 3 is quoted, with inversion symmetry replacing 4. Those thickness-dependent symmetry changes are central to the allowed anomalous Hall and spin-current tensors (Zhou et al., 2021, Cui et al., 2024, Lim et al., 2023).
Epitaxial growth on topological insulators further illustrates the structural fidelity of thin FGT. In molecular-beam-epitaxy-grown FGT on Bi5Te6, scanning tunneling microscopy resolved 7 pm and 8 pm, together with a moiré periodicity of 9 nm attributable to lattice mismatch at zero rotational misalignment. The same study identified complete-QL Te-terminated regions, double-QL regions, and partial terminations, particularly a FeGe-terminated surface with a $3d$0 reconstruction (Goff et al., 2023).
2. Magnetic order, perpendicular anisotropy, and dimensional crossover
FGT is an out-of-plane ferromagnet with strong perpendicular magnetic anisotropy (PMA), but its reported magnetic scales are strongly sample-, thickness-, and protocol-dependent. Reported bulk or bulk-like Curie temperatures include $3d$1 K from anomalous-Hall disappearance near $3d$2 K in CrSBr/FGT studies, $3d$3 K in twisted FGT/FGT junctions, $3d$4 K in nanoflake anomalous-Hall measurements, $3d$5 K in neutron powder diffraction under ambient pressure, and $3d$6 K in exfoliated FGT/Pt bilayers by Arrott-plot analysis. In thinner flakes, a Pt/FGT switching study reported $3d$7 K, and monolayer FGT was reported at $3d$8 K (Cham et al., 2023, Kim et al., 2020, Tan et al., 2018, Wang et al., 2 Apr 2025, Alghamdi et al., 2019, Wang et al., 2019, Fei et al., 2018).
The thickness dependence reveals a dimensional crossover rather than a single universal magnetic scale. For thicknesses below about $3d$9 nm, corresponding to roughly five layers, the critical behavior crosses over from 3D to 2D Ising-like. Reported critical exponents from remanent magneto-optical measurements are 0 for thick flakes, 1 for intermediate thicknesses, and 2 in the monolayer, consistent with the 2D Ising value 3. A separate finite-size-scaling analysis of nanoflakes gave a coupling length of 4 van der Waals layers and 5, indicating interlayer magnetic coupling over roughly five layers (Fei et al., 2018, Tan et al., 2018).
Reported anisotropy parameters also span a wide range, again reflecting different thicknesses and analysis schemes. Examples include 6 for a 7 nm nanoflake, 8 in micromagnetic parameterizations chosen to reproduce the “hard” magnetic character of FGT, 9 at 0 K in CrSBr-coupled heterostructures, and 1 in Lorentz-TEM studies. The anisotropy field is commonly written as
2
and several studies infer 3 of order 4 T or several tesla depending on the adopted 5 and thickness (Tan et al., 2018, Cham et al., 2023, Kumar et al., 31 Jul 2025, Peng et al., 2021).
At low temperature, FGT frequently shows square hysteresis loops and hard-magnetic behavior. Reported coercivities include 6 mT at 7 K for a 8 nm nanoflake, up to about 9 T at 0 K in atomically thin magneto-optical measurements, and a typical increase from 1 kOe at 2 K to 3 kOe at 4 K in individual FGT flakes. Thick flakes also support multidomain states: above a critical thickness of about 5 nm, an intermediate temperature regime develops labyrinthine domains with characteristic widths around 6 nm (Tan et al., 2018, Fei et al., 2018, Kim et al., 2020).
3. Berry curvature, anomalous Hall transport, and spin-current generation
The anomalous Hall effect (AHE) is one of the main diagnostics of FGT magnetism and one of its principal intrinsic transport phenomena. In transport form, the Hall response is often written as 7, while the intrinsic anomalous Hall conductivity is evaluated from the Berry-curvature Kubo formalism. One cited expression is
8
and the strain study gives the clean-limit three-dimensional form for 9 and 0 with a 1 2-mesh and a broadening 3 eV. In that work, the intrinsic anomalous Hall conductivity at the true Fermi level was reported as 4 at 5 strain, 6 at 7 armchair strain, and 8 at 9 armchair strain, leading to the conclusion that the intrinsic AHE is robust to in-plane uniaxial strain up to $0.8$0 (Lim et al., 2023, Tan et al., 2018).
That robustness is not universally consistent with all prior experimental interpretations. The same strain analysis explicitly notes disagreement with an earlier experimental report that less than $0.8$1 uniaxial strain can double the anomalous Hall resistance. Three explanations are discussed there: strain-sensitive extrinsic AHE terms, correlation effects beyond the simple DFT-level description, and concurrent changes in $0.8$2 that alter measured $0.8$3 without comparably altering $0.8$4. The authors state that this discrepancy implies that the present understanding of the AHE in FGT is incomplete (Lim et al., 2023).
FGT also supports a spin anomalous Hall effect (SAHE) whose magnitude and spin polarization depend nonlinearly on the magnetization direction. For an in-plane electric field $0.8$5, the cited definitions are
$0.8$6
with $0.8$7. In monolayer FGT, a horizontal mirror $0.8$8 forbids an out-of-plane spin current for strictly in-plane magnetization, but once the magnetization acquires a $0.8$9-component, both in-plane and out-of-plane spin-current channels become allowed. In bilayer FGT, the loss of 0 and the presence of inversion symmetry permit all three spin-polarization channels, so an intermediate magnetization direction can produce an arbitrary spin-polarization vector. A central relation derived for the intra-band part is
1
linking SAHE directly to AHE through Berry curvature weighted by the local spin expectation value (Zhou et al., 2021).
4. Spin–orbit torques and current-driven switching
FGT has been studied in both interfacial-SOT and bulk-SOT regimes. In Pt/FGT bilayers, a charge current in Pt generates a transverse spin current via the spin Hall effect and applies damping-like and field-like torques to the FGT magnetization. The torque forms quoted in the literature include
2
and the damping-like efficiency is often written as
3
In few-layer Pt/FGT Hall bars, full hysteretic switching at 4 K under 5 mT occurred for 6 mA, corresponding to 7 in Pt. Harmonic Hall analysis at 8 K yielded 9 and 0, with an inferred 1 when a reduced few-layer magnetization is assumed (Wang et al., 2019).
A separate FGT/Pt study on 2 nm flakes reported switching at 3 K with zero in-plane-bias extrapolated critical current density 4 in Pt. Second-harmonic Hall measurements gave 5 at 6 mA and 7 at 8 mA, values described there as rivaling the best metallic ferromagnet/heavy-metal stacks. That work attributes the large efficiency to the atomically flat FGT/Pt interface (Alghamdi et al., 2019).
FGT also exhibits bulk spin–orbit torques without a heavy-metal overlayer. In single FGT flakes, symmetry analysis identifies a current-induced effective field
9
and harmonic Hall measurements on a 00 nm flake gave damping-like fields up to 01. Fitting to the bulk form yielded 02 at low temperature, showing that current-driven manipulation in FGT need not rely exclusively on interfacial spin Hall injection (Martin et al., 2021).
These torque mechanisms have been extended to device architectures. An all-van-der-Waals three-terminal SOT-MRAM based on top-FGT/h-BN/bottom-FGT used the top FGT as the free layer and the bottom FGT as the pinning layer. At 03 K, the device showed an initial TMR ratio of about 04, a stable working TMR of about 05, onset of nonvolatile switching at 06 mA, and 07. The write and read current paths were physically decoupled, with in-plane mA-order writing current and vertical 08A-order read current (Cui et al., 2024).
5. Exchange bias, tilted magnetic states, and voltage-controlled switching
Exchange bias in FGT has been demonstrated in several van der Waals heterostructures and is notable because the coupled antiferromagnets can have orthogonal magnetic anisotropies. In CrSBr/FGT, the in-plane easy axis of CrSBr acts on the perpendicularly magnetized FGT through an in-plane exchange-bias field 09. The effect appears only below the CrSBr Néel temperature 10 K, rises to about 11 T at 12 K, and vanishes above 13. A CrSBr thickness greater than 14 nm is required for non-zero exchange bias at 15 K. In a macrospin picture, the FGT tilt under this orthogonal coupling is described by
16
which gives
17
Using 18 T, 19, and 20, the cited estimate is 21, consistent with the greater-than-22 tilt inferred from Hall data. In CrSBr/FGT/Pt, the same in-plane exchange bias provides sufficient symmetry breaking for deterministic spin–orbit torque switching at zero applied magnetic field (Cham et al., 2023).
A later CrSBr/FGT study linked this exchange bias to correlated domain structures rather than to a simple rigid interfacial shift. In Au/FGT 23/CrSBr 24/h-BN stacks, anomalous Hall loops at 25 K gave 26 mT after a 27 T preset and 28 mT after a 29 T preset. The bias vanished near 30 K, close to 31 K of CrSBr, and a pronounced training effect was observed: only the first sweep after preset showed asymmetric switching and nonzero 32. Off-axis electron holography on a 33-plane lamella revealed stripe-like flux-closure domains in FGT with circular rotation of the magnetic induction in the 34 plane, directly connecting asymmetric reversal to domain nucleation and annihilation (Kumar et al., 31 Jul 2025).
FGT can also host exchange bias against an antiferromagnetic oxide derived from itself. In FGT/O-FGT/hBN, where the O-FGT is formed by natural oxidation of the FGT surface, field cooling by 35 kOe from 36 K to low temperature produced an exchange-bias field 37 kOe at 38 K and a blocking temperature 39 K. The gate dependence was linear,
40
with 41. In that device, deterministic voltage-controlled magnetization reversal occurred near 42 V for stepped holds of 43 s, and the switching energy was estimated as 44 pJ per bit (Sharma et al., 2024).
6. van der Waals heterostructures, magnetoresistance, moiré interfaces, and interfacial Hall control
FGT supports several distinct magnetotransport phenomenologies depending on what is stacked against it. In twisted FGT/FGT homojunctions with 45, the interface remains metallic: the resistance decreases monotonically on cooling, from 46 at 47 K to about 48 at 49 K, and the 50–51 characteristics are linear up to 52 mV. The magnetotransport shows a plateau-like magnetoresistance defined by
53
arising from antiparallel switching of the two FGT layers. The PMR grows from about 54 at 55 K to about 56 at 57 K. The same study emphasizes that this is at least three orders of magnitude smaller than typical TMR, consistent with a clean metallic junction rather than a tunnel barrier (Kim et al., 2020).
In FGT/graphite/FGT trilayers, the reported response is qualitatively different from conventional two-state giant magnetoresistance. The devices show three distinct resistance states: a high-resistance antiparallel “OUT” configuration, an intermediate parallel state, and a low-resistance antiparallel “IN” configuration. At 58 K, the MR amplitude 59 reaches about 60 depending on device and is essentially independent of graphite thickness between 61 and 62 nm. The proposed mechanism is spin-momentum-locking-induced spin-polarized current at the graphite/FGT interfaces rather than standard spacer-mediated GMR (Albarakati et al., 2019).
FGT also forms structurally clean interfaces with topological insulators. In monolayer FGT grown on Bi63Te64, the moiré wavelength satisfies
65
in agreement with the measured 66 nm. The topological surface state of Bi67Te68 remained visible through quasiparticle interference, and magnetic circular dichroism on thin FGT/Bi69Te70 films showed a square hysteresis loop at 71 K with coercivity around 72 Oe and 73 K (Goff et al., 2023).
A different interfacial control mode appears in WTe74/FGT. Applying a current through 75-WTe76 modulates the AHE of adjacent FGT, with a relative change in AHE conductivity exceeding 77. The effect is absent in pure FGT, weakens as the FGT becomes thicker, and peaks for bilayer WTe78, which the authors attribute to a Berry-curvature-dipole mechanism in WTe79 and an inverse magnetic proximity effect on FGT. For one device, 80 at zero modulation current, rises to about 81 by 82 mA, and is suppressed to nearly zero near 83 mA (Guo et al., 7 Jan 2026).
7. Domain textures, skyrmion bubbles, and external tuning
FGT supports multiple nonuniform magnetic states, and those states depend strongly on thickness, interfaces, and field history. In thicker flakes, labyrinthine domains appear in an intermediate temperature window, with typical domain widths around 84 nm. In Lorentz-TEM studies of 85 FGT thin plates, the zero-field-cooled ground state below about 86 K consists of stripe domains with period 87 nm. Under a perpendicular field at 88 K, the stripes begin to break into mixed fragments and isolated bubbles near 89 Oe, form fully developed skyrmion bubbles by about 90 Oe, and collapse to a uniform state above 91 Oe. A field-cooling protocol with 92 Oe generated a hexagonal lattice with bubble diameters of about 93 nm and lattice constant 94 nm (Fei et al., 2018, Ding et al., 2019).
The topological charge of those bubbles is described by
95
and transport-of-intensity reconstructions in the cited work are consistent with Bloch-type chirality and 96 per bubble. An important point is that the micromagnetic model used for these FGT skyrmion bubbles did not require a DMI term: the textures were modeled from exchange, uniaxial anisotropy, Zeeman coupling, and dipolar energy in a centrosymmetric material. By contrast, in Pt/oxidized-FGT/FGT/oxidized-FGT heterostructures, interfacial DMI favors Néel-type walls. Lorentz-TEM showed that under 97 mT the modulation wavevector 98 is perpendicular to the in-plane field in the heterostructure, whereas in an FGT plate without heavy-metal capping, 99 is rotated by $3d$00, giving fan-like modulations characteristic of Bloch-like twists (Ding et al., 2019, Peng et al., 2021).
FGT is also unusually tunable by pressure and chemical modification. Under hydrostatic pressure up to $3d$01 GPa, neutron diffraction found no structural phase transition but a monotonic suppression of ferromagnetism: $3d$02 decreases from $3d$03 K at $3d$04 GPa to $3d$05 K at $3d$06 GPa, with a slope $3d$07. The Fe(1) ordered moment at $3d$08 K decreases from $3d$09 to about $3d$10 by $3d$11 GPa, and the interpretation is that shorter Fe–Fe distances strengthen direct antiferromagnetic exchange while changes in Fe–Te–Fe and Fe–Ge–Fe angles weaken ferromagnetic superexchange (Wang et al., 2 Apr 2025).
Chemical intercalation can shift the system in the opposite direction. Electrochemical insertion of tetrabutylammonium cations into Fe$3d$12GeTe$3d$13 yields Fe$3d$14GeTe$3d$15(TBA)$3d$16 with $3d$17 per formula unit, injects roughly one electron per formula unit, and stabilizes a room-temperature ferromagnetic phase with $3d$18 K, compared with $3d$19 K in the same study. Raman spectra show $3d$20 red shifts of the $3d$21 and $3d$22 modes after intercalation, while vdW-corrected ab initio calculations indicate increased density of states at $3d$23, enhanced nearest-neighbor $3d$24 by about $3d$25, and reduced magnetocrystalline anisotropy energy. This suggests that FGT is not defined by a single fixed magnetic parameter set; rather, it is a tunable itinerant ferromagnet whose ordering temperature, anisotropy, domain morphology, and transport response can be substantially reconfigured by thickness, interface design, pressure, gating, and intercalation (Iturriaga et al., 2022).
