{"id":"0ee819d9-0d7a-4fe7-9d71-cca18699e484","arxiv_id":"2502.05018","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":4.0,"correctness_risk":"high","formal_verification":"none","parameter_count":3,"one_line_summary":"A cusp-shaped Hall response under in-plane magnetic fields in Fe3GeTe2 nanoflakes is attributed, via atomistic simulations, to thermally assisted frustrated spins and nonzero scalar spin chirality.","lead":"This paper measures how electrical Hall signals respond to magnetic fields in thin flakes of Fe3GeTe2 and cobalt-doped Fe3GeTe2. The authors propose that an unusual in-plane-field cusp comes from competing magnetic interactions and thermal fluctuations creating a nonzero scalar spin chirality, a picture relevant for 2D spintronics.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The claimed chirality origin of the Hall cusp is not established: Eq. (2) defines χ as an absolute value, and no transport calculation or signed-chirality average is supplied, so the plotted |χmZ| cannot be assumed to produce a net Hall signal.","rationale":"The reader identified the same broad gap: the link between computed scalar spin chirality and measured Hall resistance is assumed, not derived. My concern is a sharper, more internal version of that gap: Eq. (2) computes an absolute value, and the relevant transport quantity would be the net signed chirality. Since the model Hamiltonian has no DMI (the authors find it cancels between monolayers) and no other chirality-selecting term, mirror symmetry of the lattice may force the signed chirality to average to zero; if so, the plotted |χmZ| peak has no direct relation to a Hall voltage. This is not an attack on the experimental data or on the atomistic model itself; the cusp is real and the model may be relevant. The concern is that the central mechanistic claim is unsupported as written and needs either a signed-chirality calculation or a transport calculation connecting the spin texture to Rxy. The reader's CONDITIONAL verdict remains appropriate, with the condition made explicit: specify bijk and demonstrate that a net chirality-induced emergent field survives thermal and disorder averaging. This is why I recommend UNCHANGED rather than ACCEPT or REJECT; the paper can be made sound with additional analysis, but in its current form the central claim is not established.","tokens_in":8217,"tokens_out":12221,"duration_ms":156853,"concrete_test":"Run the atomistic simulation at the reported peak fields and temperatures and compute the thermal average of the signed chirality C_net = (1/2)⟨Σ bijk Si·(Sj×Sk)⟩ without the absolute value, over long Monte Carlo or Langevin trajectories and several disorder or initial-condition realisations. Report both C_net and |C|; if C_net averages to zero or is orders of magnitude smaller than the plotted |χ| while |C| peaks, the proposed net emergent-field mechanism is falsified.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim requires that the computed scalar spin chirality produces the measured transverse voltage, but Eq. (2) defines χ = (1/2)|Σ bijk (Si·Sj×Sk)| with bijk unspecified, and the paper never derives how this quantity enters Rxy. The absolute value is the critical problem: a fictitious field contributing to the Hall voltage is generated by the net chirality, whereas |χ| counts local non-coplanarity even when contributions from different triangles cancel. The Hamiltonian in Eq. (1) contains only Heisenberg exchange, uniaxial anisotropy, and Zeeman coupling, and the authors themselves find that DMI cancels between adjacent monolayers (Sec. S6). With no chirality-selecting interaction, the thermal average of the signed chirality is expected to vanish by the mirror symmetry of the triangular lattice, or at least must be shown to be nonzero; the positive quantity plotted in Fig. 4(a) cannot simply be equated to an emergent magnetic field. Even granting a nonzero χ, the statement that '|χmZ| corresponds to the fictitious internal magnetic field along the c-axis' is an assumption, not a derivation. Alternative explanations for the cusp-like Rxy(Hx), such as coherent Stoner-Wohlfarth rotation of mz, planar Hall leakage, or contact misalignment, are dismissed without quantitative comparison. Thus the leap from Fig. 4(b) to the measured Hall cusp is the weakest load-bearing step.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript reports magnetotransport measurements on exfoliated Fe3GeTe2 and (Co0.25Fe0.75)3GeTe2 nanoflake devices. For out-of-plane magnetic fields the devices show square anomalous Hall loops; for in-plane fields the Hall resistance shows a cusp-like feature that the authors attribute to thermally assisted frustrated spin configurations with nonzero scalar spin chirality, which they argue produces an effective out-of-plane fictitious field. Atomistic spin simulations based on a Heisenberg Hamiltonian with exchange, anisotropy, and Zeeman terms are used to compute the scalar spin chirality, and the product |chi mZ| is compared qualitatively with the measured RXY(Hx). The paper concludes that competitive antiferromagnetic and ferromagnetic interactions combined with thermal fluctuations lead to the observed cusp via frustrated non-coplanar spin configurations.","tokens_in":8575,"tokens_out":4098,"duration_ms":45166,"significance":"If the interpretation is correct, the cusp would be an electrical signature of frustration-induced scalar spin chirality in a few-layer van der Waals ferromagnet, which would be of interest for 2D spintronics and for understanding non-collinear spin textures in reduced dimensions. The experimental work is substantial: it includes crystal growth, device fabrication, magnetization characterization, and atomistic modeling with experimentally determined anisotropy constants. However, the central link between the computed chirality and the measured Hall resistance is not established, and the current evidence is only qualitative. The paper would be significantly strengthened by a proper transport calculation connecting chirality to RXY and by quantitative comparison with the data.","major_comments":[{"comment":"Equation (2) defines chi = (1/2) |sum bijk (Si . Sj x Sk)|, but a Hall response requires the net signed scalar spin chirality, not the absolute value of the sum. If contributions from different triangles cancel, the plotted |chi| cannot be interpreted as an emergent fictitious field. Because the Hamiltonian in Eq. (1) contains no chirality-breaking term and the authors state in Sec. S6 that the DMI cancels between adjacent monolayers, the thermal average of the signed chirality may vanish by the mirror symmetry of the triangular lattice; the authors must compute the sign-resolved chirality, demonstrate that its thermal average is nonzero, and specify the coefficient bijk.","section":"Eq. (2) and Sec. S6"},{"comment":"The manuscript does not derive how chi or |chi mZ| enters the Hall resistance. The statement that |chi mZ| corresponds to a fictitious internal magnetic field is an assumption, not the result of a transport calculation. Without a Boltzmann or Berry-curvature expression connecting the chirality to a transverse conductivity, the qualitative peak matching in Fig. 4(b) against Fig. 3(c,d) does not establish the proposed mechanism. Please provide a derivation or a quantitative model showing that RXY is proportional to the computed chirality-weighted magnetization.","section":"Sec. 4, Fig. 4(b)"},{"comment":"The comparison between calculation and experiment is only qualitative: the text states that the peak of |chi mZ| appears at similar values of HX, but no fitting, error bars, or scale comparison is provided. Moreover, Fig. 4 shows only FGT, while the claimed threshold-field behavior of Co0.25FGT is discussed without a corresponding calculation. The paper should quantify the threshold fields for both compounds, include uncertainties, and compare the predicted temperature dependence with the measured RXY(Hx) curves.","section":"Fig. 4 and Fig. 3(c,d)"},{"comment":"Stoner-Wohlfarth rotation, planar Hall leakage, and contact misalignment are dismissed in a single sentence without quantitative analysis. Any of these can produce a cusp-like RXY(Hx), so the paper needs estimates of their magnitudes, such as the planar Hall coefficient and the possible misalignment angle, to exclude them as the origin of the observed feature.","section":"Sec. 3, discussion of alternative mechanisms"}],"minor_comments":[{"comment":"The summation indices in Eq. (1) are typeset inconsistently, with stray subscripts in the displayed formula; please clean up the notation.","section":"Eq. (1)"},{"comment":"The caption lists panels (c), (f) twice, and the mapping of panels to FGT and Co0.25FGT magnetization curves is confusing; please renumber the panels and make the correspondence explicit.","section":"Fig. 1 caption"},{"comment":"The measurement geometry for RXY under in-plane field should be specified more precisely, including contact separation and aspect ratio, and the authors should state whether the Hall signal was antisymmetrized to remove longitudinal contamination.","section":"Fig. 3(c,d)"},{"comment":"Figure 4 shows only FGT; if the Co0.25FGT calculation is unavailable, state this explicitly, or add the corresponding curves to support the qualitative discussion.","section":"Fig. 4"}],"recommendation":"major_revision","confidential_remarks":"The manuscript overlaps with the authors' earlier bulk studies (Refs. 18 and 19), so the novelty hinges on the claim that dimensional reduction changes the origin of the cusp. The refereeing process should require signed-chirality calculations and a transport model connecting chirality to RXY; otherwise the central claim remains unsupported. If these cannot be supplied in a revision, rejection may be more appropriate."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The cusp in Rxy(Hx) is real and the DMI-cancellation calculation is a good check, but the chirality origin is asserted, not derived. If I were the editor, I'd send it out, but the theory needs major work.\n\nWhat's genuinely new: exfoliated flakes of FGT and Co0.25FGT, around 28–33 nm thick, clean square AHE for H along c, and a cusp-like Hall feature for H in-plane. The threshold field shifts with Co doping, consistent with weakened exchange and anisotropy. The atomistic model uses measured anisotropy constants and includes both AFM and FM exchange; the result that DMI cancels between adjacent monolayers is a useful, non-obvious observation that correctly rules out one class of explanations.\n\nThe soft spot is the central claim. Equation (2) defines χ as 1/2 |Σ bijk (Si·Sj×Sk)|, with bijk never specified. That absolute value is not a benign detail. A fictitious field from scalar spin chirality comes from the net signed chirality; |χ| counts local non-coplanarity even when triangle contributions cancel. With DMI cancelled and only Heisenberg exchange, uniaxial anisotropy, and Zeeman coupling in the Hamiltonian, the mirror symmetry of the triangular lattice should make the thermal average of the signed chirality vanish unless that symmetry is broken. The paper never shows a nonzero net chirality. Nor does it show how χ enters Rxy: there is no transport calculation, and the comparison in Fig. 4(b) is just peak-position matching. The qualitative agreement is suggestive, but the plotted |χ mZ| cannot simply be equated to an effective magnetic field.\n\nThe alternative explanations—planar Hall leakage, contact misalignment, Stoner–Wohlfarth rotation of mz—are dismissed without quantitative comparison. That may be fine if the theory were solid, but it isn't. The experimental data also lack error bars on the cusp positions, so the claimed systematic shift with T and doping is not as firm as the text implies.\n\nBottom line: the experiment is worth reporting and the model is worth refining, but the inference from |χ mZ| to the Hall signal is a load-bearing assumption. A serious referee should engage with it, and I'd expect heavy revision before publication.","headline":"The cusp is real and the DMI-cancellation check is useful, but the chirality origin is asserted, not derived; the paper deserves referee time but needs major theory revision.","tokens_in":9106,"tokens_out":2431,"would_cite":false,"duration_ms":26221,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"This paper claims that the cusp in the Hall resistance of few-layer Fe3GeTe2 and cobalt-doped Fe3GeTe2 under in-plane field is a transport signature of frustrated spin chirality acting as a fictitious out-of-plane field.","keywords":["Fe3GeTe2","scalar spin chirality","magnetic frustration","anomalous Hall effect","magnetotransport","van der Waals magnets","atomistic spin model","nanoflake devices"],"falsifier":"Compute the Hall conductivity from the atomistic spin configurations with a Berry-curvature transport formula and compare its in-plane-field dependence with the measured cusp; if the calculated Hall signal has no peak where $|\\chi m_Z|$ peaks, or a spin-resolved imaging measurement shows the spins staying collinear across the cusp field, the chirality explanation would be falsified.","tokens_in":8069,"feed_emoji":"🧲","tokens_out":10635,"duration_ms":93322,"temperature":0.7,"pith_summary":"The paper asks what produces an unusual cusp in the Hall resistance of few-layer Fe3GeTe2 and cobalt-doped Fe3GeTe2 devices when the magnetic field is applied in the plane rather than along the easy axis. It argues that the cusp is not a conventional planar Hall effect or a Stoner-Wohlfarth reversal, but a signature of magnetic frustration: competing ferromagnetic and antiferromagnetic interactions, helped by thermal fluctuations, stabilize non-coplanar spin configurations whose scalar spin chirality $\\chi$ creates an effective out-of-plane field. Atomistic spin-model calculations produce a peak in $|\\chi m_Z|$ at the same in-plane field values where the measured Hall cusp appears. If correct, this gives a transport-based electrical readout of frustration-induced spin chirality in a van der Waals ferromagnet, relevant to non-collinear spin textures and spintronic devices.","feed_headline":"Hall cusp in Fe3GeTe2 tied to frustrated spin chirality","feed_subtitle":"If right, a simple Hall measurement can detect magnetic frustration in two-dimensional magnets.","key_machinery":"The central object is the scalar spin chirality $\\chi$, defined as half the absolute value of the sum of mixed products $b_{ijk}\\,\\mathbf{S}_i \\cdot (\\mathbf{S}_j \\times \\mathbf{S}_k)$ over neighboring spin triples. It measures how non-coplanar the spin texture is, and nonzero values couple to conduction electrons like an emergent magnetic field. The atomistic calculation evaluates $\\chi$ in a Heisenberg Hamiltonian that includes ferromagnetic and antiferromagnetic exchange, uniaxial anisotropy, and the Zeeman energy of an in-plane field, and it also computes domain energies and the interlayer cancellation of Dzyaloshinskii-Moriya interactions. In the paper's picture, the product $|\\chi m_Z|$ is the fictitious out-of-plane field whose peak in field sweeps marks the Hall cusp.","core_discovery":"Applying the magnetic field along the c-axis of few-layer Fe3GeTe2 (FGT) and (Co0.25Fe0.75)3GeTe2 (Co0.25FGT) devices produces square anomalous Hall hysteresis, while an in-plane field produces an unusual cusp in the Hall resistance that cannot be explained by the Stoner-Wohlfarth model or the planar Hall effect. The paper's central claim is that the cusp is the electrical signature of thermally assisted magnetic frustration: the Fe atoms form a triangular lattice with intraplanar antiferromagnetic coupling stabilized into a ferromagnet by interplanar exchange, and the resulting competition, aided by thermal fluctuations, produces non-coplanar spin configurations with non-zero scalar spin chirality $\\chi = \\frac{1}{2}\\left|\\sum b_{ijk}\\,\\mathbf{S}_i \\cdot (\\mathbf{S}_j \\times \\mathbf{S}_k)\\right|$. This chirality acts as a fictitious out-of-plane magnetic field, so the measured Hall resistance rises at low in-plane fields and falls once the spins align in the plane. The paper also shows that Dzyaloshinskii-Moriya interactions cancel between adjacent monolayers, leaving frustration as the operative mechanism, and that cobalt doping lowers the in-plane field threshold because it weakens exchange and anisotropy.","pith_inferences":["Beyond the paper, if the interpretation is right, the same chirality-induced scattering should also show up in other transport channels, such as thermal Hall or magnon transport, where nonzero scalar spin chirality can produce transverse signals; the paper does not test this.","A direct transport calculation connecting $\\chi$ to the Hall conductivity, rather than a qualitative comparison of $|\\chi m_Z|$ with the cusp position, would turn the proposed mechanism into a quantitative prediction; this is a natural next step, not part of the paper.","The scenario predicts that other uniaxial van der Waals ferromagnets built from frustrated triangular layers should show a similar cusp under in-plane fields, so the feature could act as a general diagnostic rather than being particular to Fe3GeTe2."],"forward_implications":["In-plane Hall measurements can act as a probe of frustrated non-coplanar spin configurations in few-layer van der Waals ferromagnets.","Cobalt doping shifts the cusp to lower in-plane fields because it weakens exchange and magnetic anisotropy, so the cusp position tracks the interaction strengths.","Dzyaloshinskii-Moriya interactions play no role in these flakes because their contributions cancel between adjacent monolayers, so the cusp is not evidence for DMI-stabilized skyrmions.","Thermal fluctuations assist the effect: increasing temperature enhances the computed scalar spin chirality and moves the cusp to lower fields, so the signal should be strongest near the magnetic ordering temperature."],"supporting_citations":[{"why":"reports the cusp-like Hall behavior and material parameters for bulk FGT that this work reproduces in nanoflakes and reinterprets.","marker":"[18]"},{"why":"reports analogous cusp behavior in Co- and As-doped FGT and supplies the doping-dependent anisotropy and exchange inputs.","marker":"[19]"},{"why":"first-principles prediction of the competing intraplanar antiferromagnetic and interplanar ferromagnetic interactions that ground the frustration picture.","marker":"[22]"},{"why":"supplies the concept of scalar spin chirality producing an effective pseudo-magnetic field via Berry curvature.","marker":"[23]"},{"why":"supplies the mechanism by which nonzero scalar spin chirality acts as a scattering source for conduction electrons, connecting chirality to transport.","marker":"[24]"},{"why":"attributes the anomalous Hall effect along the easy axis in FGT to topological nodal lines, providing the baseline for interpreting the out-of-plane-field data.","marker":"[26]"},{"why":"documents Dzyaloshinskii-Moriya interaction and topological spin textures in FGT, the alternative mechanism the calculations exclude.","marker":"[29]"},{"why":"shows DMI-driven chiral textures in another van der Waals magnet, supporting the need to test and rule out a DMI origin for the cusp.","marker":"[30]"},{"why":"provides the atomistic spin Hamiltonian and calculation framework used to evaluate spin chirality.","marker":"[31]"}],"fun_headline_variants":["Hall cusp reveals frustrated spins in 2D magnet","Frustration-induced chirality spotted in Hall signal","Fe3GeTe2 cusp ties Hall effect to spin frustration","Thermally assisted frustration creates Hall cusp in 2D magnet","Scalar spin chirality leaves Hall cusp in Fe3GeTe2"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that the calculated nonzero scalar spin chirality is actually what produces the measured Hall cusp, because the paper offers a qualitative match of field values but no transport calculation connecting the two.","fun_headline_variants_meta":{"raw":{"variants":["Hall cusp reveals frustrated spins in 2D magnet","Frustration-induced chirality spotted in Hall signal","Fe3GeTe2 cusp ties Hall effect to spin frustration","Thermally assisted frustration creates Hall cusp in 2D magnet","Scalar spin chirality leaves Hall cusp in Fe3GeTe2"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000348,"raw_usage":{"total_tokens":1944,"prompt_tokens":1025,"completion_tokens":919,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":641,"completion_tokens_details":{"reasoning_tokens":830}},"tokens_in":641,"tokens_out":919,"duration_ms":9060,"temperature":1.0,"reasoning_tokens":830,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-08T20:33:39.564673+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Compute the Hall conductivity from the atomistic spin configurations with a Berry-curvature transport formula and compare its in-plane-field dependence with the measured cusp; if the calculated Hall signal has no peak where $|\\chi m_Z|$ peaks, or a spin-resolved imaging measurement shows the spins staying collinear across the cusp field, the chirality explanation would be falsified.","supporting_citations":[],"review_version":1}