REVIEW 4 major objections 5 minor 47 references
Room temperature observation of the anomalous in-plane Hall effect in epitaxial thin films of a Weyl ferromagnet
T0 review · 4 major / 5 minor · reviewed 2026-08-10 · deepseek-v4-flash
Pith's one-line read A spin-canted kagome Weyl ferromagnet, Fe3Sn, exhibits an anomalous in-plane Hall effect at room temperature whose temperature-independent magnitude across 100–300 K identifies it as an intrinsic Berry-curvature response.
desk verdict A credible room-temperature in-plane Hall effect in Fe3Sn, but the bulk topological origin is undercut by an internal inconsistency in the thickness-scaling argument. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The load-bearing symmetry is the magnetic glide-mirror operation combining an out-of-plane mirror, a fractional translation, and time reversal; when the magnetization lies strictly in the plane, this symmetry forces the Berry curvature to integrate to zero, while an out-of-plane canting Mz breaks it and permits a finite Berry curvature and thus a finite anomalous in-plane Hall effect. The experimental machinery is a circular Hall bar that allows the full 2π angle dependence of the transverse resistivity to be decomposed into a field-antisymmetric in-plane Hall effect, a symmetric planar Hall effect, and a symmetric transverse resistivity, isolating the true Hall signal from artefacts. The temperature independence of the extracted conductivity serves as the fingerprint that the signal is intrinsic (Berry-curvature) rather than extrinsic (skew scattering or side jumps).
What would settle it
A neutron diffraction experiment on bulk Fe3Sn crystals or on a sufficiently thick film that finds no out-of-plane component of the ordered magnetic moment below the ordering temperature would directly falsify the symmetry-breaking premise; alternatively, measuring the same in-plane Hall protocol on a sample with a verified strictly in-plane magnetization and zero remanent out-of-plane moment should show no 2π-periodic field-antisymmetric signal if the proposed mechanism is the only source.
Extended reading notes
Core claim
The central claim is that Fe3Sn thin films with in-plane ferromagnetism and a finite out-of-plane spin canting exhibit an anomalous in-plane Hall effect whose magnitude is independent of temperature between 100 and 300 K, which the authors identify as the hallmark of an intrinsic Berry-curvature contribution from Weyl points near the Fermi energy. In an uncanted ferromagnet with magnetization along the x direction, the magnetic space group contains a glide-mirror operation that enforces cancellation of the Berry curvature, so the in-plane Hall conductivity vanishes. A canting along z breaks this operation and makes the total Berry curvature finite, producing an in-plane Hall conductivity of about 0.8 S/cm, in reasonable agreement with the calculated value. A circular 12-terminal Hall bar that rotates the current direction relative to the in-plane field reveals the predicted 2π-periodic modulation, a π shift between opposite current directions, and a negligible ordinary anomalous Hall offset; thickness scaling indicates the effect comes from the bulk of the film rather than the interface. Adding a CoFeB layer with a stray-field component along z increases the measured amplitude by roughly 38%, demonstrating external control of the effect.
Load-bearing premise
The argument stands on the premise that the tiny out-of-plane remanent moment measured in the films, about 0.11 Bohr magneton per iron atom, is a uniform tilt of the magnetic moments through the bulk of the film, rather than an interface-only effect or a measurement artefact, because only a bulk tilt breaks the symmetry that the transport claim requires.
Editorial extensions
If this is right
- If the claim is correct, topological Hall effects no longer need cryogenic temperatures: kagome magnets with large exchange interactions can deliver Berry-curvature Hall signals at and above 300 K.
- The circular Hall bar with full angle decomposition provides a template for separating true in-plane Hall effects from planar-Hall and misalignment artefacts, which can be applied to other candidate materials.
- The 38% enhancement by a CoFeB stray field demonstrates a practical route to tune the in-plane Hall amplitude in a topological heterostructure, suggesting that magnetic stray fields from adjacent layers can serve as a control knob.
- A temperature-independent in-plane Hall conductivity between 100 and 300 K can be used as a fast diagnostic for intrinsic topological contributions in future materials.
- The symmetry rule, to break the out-of-plane glide-mirror operation via canting, becomes a design criterion: canted kagome ferromagnets with strong exchange are candidate room-temperature in-plane Hall materials.
Reading between the lines
- The same symmetry-breaking logic likely applies to other magnetic Weyl systems with easy-plane anisotropy and a tunable canted moment, making Fe3Sn a first member of a broader family rather than an isolated case.
- If neutron scattering confirms the bulk canting, the temperature-independent in-plane Hall plateau could serve as a sensitive probe of the canting angle, because the conductivity should scale with Mz in the small-canting limit.
- The heterostructure demonstration is only a proof of concept; optimizing the spacer thickness and the stray-field geometry could push the enhancement well beyond 38%, and the same mechanism might also tune the nonlinear Hall effect in these films.
- One caution follows from the authors' own note: the magnetic structure is not yet measured directly, so the precise quantitative link between the canting moment and the measured conductivity remains to be established by a microscopic probe rather than inferred from transport alone.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript reports molecular-beam-epitaxial growth of Fe3Sn(001) films on Pt(111)/sapphire, fabrication of circular Hall bars, and measurements of the in-plane Hall response at 300 K. By antisymmetrizing the transverse resistivity in B∥, the authors isolate a 2π-periodic, B-antisymmetric in-plane Hall resistivity ρ_IPHE(ϕ,θ), separate it from the symmetric planar-Hall and STR contributions, and find the amplitude to be nearly field-independent below 100 mT, temperature-independent between 100 and 300 K with |σ0_IPHE| ≈ 0.8 S/cm, and roughly consistent with the film thickness. They interpret the effect as an anomalous IPHE driven by Weyl-point Berry curvature enabled by an out-of-plane canting Mz ≈ 0.11 μB/Fe that breaks the MztT magnetic-glide symmetry, and they report a ≈38% enhancement in a Fe3Sn/Al2O3/CoFeB heterostructure. DFT/Wannier calculations with a canted magnetization and a Zeeman term yield a 2π-periodic σ_IPHE(α) of order 1.5 S/cm.
Significance. If established, the result would be the first room-temperature, temperature-independent anomalous in-plane Hall effect from topological electronic states, with a plausible design paradigm for tuning it. The paper is commendable for its angle-resolved circular-Hall-bar methodology, the explicit separation of symmetric and antisymmetric responses, and the internal checks of field independence and thickness scaling. However, the theoretical calculation is not parameter-free, and the experimental identification of a uniform bulk canting rests on indirect evidence; these issues must be resolved before the central claim can be accepted.
major comments (4)
- [Methods, 'Anomalous in-plane Hall effect calculated using the Wannier tight-binding model'] The central theoretical claim is not parameter-free. In the effective Hamiltonian H = H0 + gB∥·σ, the authors insert a canting M = (1, 0, 0.1) and choose gB∥ = 0.001 eV; since this canting breaks MztT by construction, the resulting nonzero σ_IPHE is guaranteed by symmetry (the authors themselves state that σ_IPHE vanishes without canting). Therefore the statement in the 'Origin' section that |σ0_IPHE| ≈ 0.8 S/cm is in 'relatively good quantitative agreement' with |σcalc_IPHE| ≈ 1.5 S/cm is not a meaningful test unless the authors show the sensitivity to the canting angle, the effective g, and the chemical potential. I request a parameter-dependence study or a fully ab initio calculation with the experimental Mz as the only input, and a discussion of whether the calculated value is robust.
- [Fig. 4(d) and 'Origin of the in-plane Hall effect'] The thickness-scaling argument as written is internally inconsistent and does not establish a bulk origin. The text states VIPHE(60 nm)/VIPHE(30 nm) ≈ 2.5 and that 'VIPHE scales approximately with the thickness of the film,' but the fitted amplitudes in the same paragraph and Fig. 4(d) are (2.9 ± 0.1) µV and (7.4 ± 0.2) µV, so the ratio is 2.9/7.4 ≈ 0.39, not 2.5. For a uniform bulk ρ_IPHE at fixed bias current, the transverse voltage scales as V ∝ 1/d, so the measured V30/V60 ≈ 2.55 is actually consistent with a bulk effect; however, the quoted ratio reverses this conclusion. Moreover, the test cannot cleanly exclude a fixed-thickness interface source in a parallel-conduction geometry, whose scaling prediction is separated from the bulk prediction by only a factor of two, and an interface layer whose thickness scales with the total film thickness would reproduce the bulk ratio. The authors should re-analyze the thickness data with a proper current-distribution model and state the actual fitted ratio.
- [Experimental detection of spin-canted ferromagnetism, Fig. 2(c)] The only direct evidence for the out-of-plane canting is the remanent Mz ≈ 0.11 μB/Fe in Fig. 2(c). The inference that this reflects a uniform bulk canting (rather than a near-interface Dzyaloshinskii-Moriya canting, a small population of misaligned domains, or an extrinsic surface moment) is based on the thickness scaling discussed above and on the bulk-like resistivity; it is not conclusive. Since the entire symmetry argument for the topological IPHE requires that MztT be broken by the bulk magnetic structure, the authors need either direct magnetic-structure determination (they themselves note that neutron scattering on bulk crystals is needed) or additional transport tests that distinguish bulk from interface canting, such as a Hall signal scaling with total magnetic moment versus interface area.
- [Fig. 4(b) and 'Origin of the in-plane Hall effect'] The temperature independence of σ_IPHE between 100 and 300 K is presented as the key evidence for an intrinsic Berry-curvature mechanism, but it is shown at a single field and angle (B∥ = 50 mT, ϕ = π, θ = π/2). The authors invoke a magnetic-field-misalignment orbital Hall contribution to explain the growth of the IPHE for B∥ ≥ 100 mT; because this same misalignment is present at lower fields, the analysis should demonstrate that the 50 mT data used for the temperature dependence lie in a regime where this orbital contribution is negligible at all temperatures, not only at 300 K. For example, measuring σ_IPHE(T) at several B∥ below 100 mT and confirming identical plateaus would make the intrinsic-origin claim more robust.
minor comments (5)
- [Data availability statement] The data availability statement contains the placeholder 'link XXX'; the actual deposition link should be provided before publication.
- [Experimental detection section] The cross-reference 'c.f. Fig. 1(c)' should refer to Fig. 2(c), where the magnetization measurements are shown.
- [Experimental detection section] The phrase 'hysteresis in both the orbital Hall and magnetization measurements' is confusing; the out-of-plane Hall resistivity is the conventional Hall effect, not the orbital Hall effect, which is introduced later as a distinct mechanism.
- [Fig. 5(e) caption] The caption reads 'Shown is a the θ dependence'; it should read 'Shown is the θ dependence.'
- [Heterostructure section] The phrase 'topological heterostructure structure' should read 'topological heterostructure.'
Circularity Check
No significant circularity: the theoretical model inputs spin canting and a Zeeman coupling, but these are not fitted to the measured IPHE, and the central experimental claim is independent.
full rationale
The paper's central claim is an experimental observation: a B-antisymmetric in-plane Hall resistivity at 300 K with a temperature-independent conductivity of about 0.8 S/cm. The theoretical section uses a Wannier tight-binding model with two inputs: an out-of-plane canting M = (1,0,0.1) and an effective Zeeman coupling gB = 0.001 eV. A nonzero sigma_IPHE does follow by symmetry once canting is inserted, but the magnitude (about 1.5 S/cm) is an output of a Kubo-formula calculation and is not obtained by fitting the measured IPHE. The canting input is independently suggested by magnetometry (Mz ≈ 0.11 mu_B/Fe), and the Zeeman coupling is not adjusted to reproduce the 0.8 S/cm value. Therefore the quantitative comparison is not a fitted parameter renamed as a prediction. The self-citations (e.g., Refs. [5,26,27]) are to prior kagome-materials work and are not load-bearing for the novel room-temperature IPHE claim. The paper even explicitly notes that neutron scattering on bulk crystals is needed to confirm the magnetic structure, acknowledging the main assumption. The internal inconsistency in the thickness-scaling discussion (stated ratio 2.5 versus fitted amplitudes giving 2.9/7.4 ≈ 0.39) is a data-analysis or presentation issue, not a circularity: it weakens the bulk-canting inference but does not reduce the IPHE result to the model's inputs. Hence no specific circular reduction can be exhibited.
Assumptions & free parameters
free parameters (3)
- Model canting ratio Mz/Mx =
0.1 (normalized, Fig. 1(e,f))
- Effective Zeeman coupling gB =
0.001 eV (Methods)
- Angular offset delta in rho_IPHE fits =
listed in Supplementary Section V
assumptions (5)
- domain assumption The Wannier/DFT band structure of Fe3Sn and its Weyl points near the Fermi energy are accurate as imported from prior calculations [20].
- domain assumption The measured out-of-plane remnant moment Mz about 0.11 Bohr magneton per Fe atom represents a uniform bulk spin canting that breaks the Mz t T symmetry, not an artifact of field misalignment, interfacial DM canting, or a surface effect.
- domain assumption The Pt(111) buffer layer shunting is negligible for the transverse voltages at all temperatures.
- domain assumption The B-antisymmetric signal at B below 100 mT contains a negligible orbital Hall contribution from out-of-plane field misalignment; OHE becomes visible only at 100 mT and above.
- standard math The Kubo formula relating Berry curvature to anomalous Hall conductivity is valid for this calculation.
Cite this review
Pith. "Pith review of Room temperature observation of the anomalous in-plane Hall effect in epitaxial thin films of a Weyl ferromagnet." pith.science (2026). https://pith.science/paper/EOFSDZCY
@misc{pith2026250113602,
author = {Pith},
title = {Pith review of: Room temperature observation of the anomalous in-plane Hall effect in epitaxial thin films of a Weyl ferromagnet},
year = {2026},
howpublished = {\url{https://pith.science/paper/EOFSDZCY}},
note = {Machine review of arXiv:2501.13602}
}
abstract
Topologically nontrivial electronic states can give rise to novel anomalous Hall effects. The potential appearance of these effects at room temperature holds promise for their application in magnetic sensing, spintronics, and energy harvesting technology. The anomalous in-plane Hall effect (IPHE) is predicted to arise in topological magnetic materials when an external magnetic field is applied within the sample plane. Because of stringent symmetry requirements, the conclusive detection of the anomalous IPHE induced by topological electronic states remains challenging, and the study of anomalous Hall effects is often confined to cryogenic conditions. Combining molecular beam epitaxy of the kagome metal Fe$_3$Sn with measurements of the electric Hall effect and theoretical calculations, we propose and experimentally demonstrate that the interplay of the kagome lattice motif with spin-orbit coupling and canted ferromagnetism with large exchange interactions gives rise to the anomalous IPHE at room temperature that is induced by topological Weyl points in the electronic band structure. Synthesizing a topological heterostructure including layers of Fe$_3$Sn and ferromagnetic CoFeB, we further show the enhancement of the anomalous IPHE through the magnetic stray field of the CoFeB layer. Our work establishes a design paradigm for topological magnets and heterostructures to discover and control novel anomalous Hall effects toward their use in technological applications.
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Reviewed August 10, 2026 · model on record in the stance chip above.
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