{"id":"b2423f79-2da3-4c82-ba2b-425f8894ff63","arxiv_id":"2507.12777","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":6,"one_line_summary":"Temperature-dependent intrinsic anomalous Hall conductivity in Fe3Ge is traced to spin reorientation of the magnetic easy axis.","lead":"Fe3Ge, a ferromagnetic kagome metal, shows anomalous Hall conductivity that changes with temperature as its magnetic easy axis rotates from out-of-plane to in-plane. This gives a rare experimental window into how band-structure Berry curvature, not just scattering, can make the Hall effect temperature dependent.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The experimental evidence for T-dependent intrinsic AHC rests on two-block TYJ intercepts (Eq. 5), but without reported slopes/errors and with an inconsistent subtraction (b=112 S/cm used for all T despite b=170 S/cm at high T), the intercept shift may be a fitting artifact.","rationale":"The paper provides credible qualitative support: magnetization shows the spin reorientation, and DFT (Fig. 4) shows the intrinsic AHC changes with angle in the same sense as the observed intercept changes. But the experimental data are strong only to the extent the TYJ decomposition isolates a constant intrinsic term. The decomposition fails to rule out that the change in b is caused by a temperature-dependent extrinsic slope. The reported subtraction inconsistency (b=112 for all T) compounds the problem. Thus the quantitative claim is not yet established; the manuscript deserves conditional acceptance pending the requested analysis and data deposition.","tokens_in":12065,"tokens_out":15759,"duration_ms":166428,"concrete_test":"From the raw data of Figs. 3(b)-(c), perform a global fit σ_A = A σ_xx^2 + b and a two-block fit with independent (A1,b1), (A2,b2); report slopes, intercepts, and 95% confidence intervals, and run an F-test for the two-block improvement. If the intercepts' CIs overlap or the F-test is not significant, the temperature dependence of the intrinsic AHC is not established. Also refit using the standard TYJ variable σ_xx instead of σ_xx^2; if a single intercept suffices, the extrinsic scaling is mis-specified.","verdict_should_be":"UNCHANGED","load_bearing_attack":"All experimental support for the central claim reduces to the two-block intercepts from Eq. 5: b changes 170→112 S/cm (in-plane) and 111→320 S/cm (out-of-plane) between high- and low-temperature blocks. In the model σ_A = A σ_xx^2 + b, b is an extrapolation to σ_xx^2 = 0; if A is temperature dependent, two-block fits can produce spurious b changes. The paper reports neither A nor confidence intervals, and does not test whether a two-block model is statistically better than a single straight line. The block split near 200 K is not tied to the 340 K spin-reorientation transition and appears post hoc. The decomposition is also internally inconsistent: to extract σ_ext_xy (Fig. 3(d)) the authors subtract the low-T b=112 S/cm at all T, while their own fit gives b=170 S/cm at high T. Thus the claimed T-dependent intrinsic AHC is not uniquely determined by the data.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports anisotropic anomalous Hall conductivity in the ferromagnetic kagome metal Fe3Ge and attributes its temperature dependence to a spin-reorientation transition that tunes the magnetization direction from out-of-plane to in-plane with decreasing temperature. The experimental Hall conductivity data are analyzed within the Tian-Ye-Jin (TYJ) scaling framework, Eq. (5), in two temperature blocks, yielding different intercepts b (170 to 112 S/cm in-plane, 111 to 320 S/cm out-of-plane) that are identified as the temperature-dependent intrinsic anomalous Hall conductivity. Density functional theory calculations with magnetization oriented at different angles reproduce the qualitative trend of a crossover between in-plane and out-of-plane intrinsic conductivity. The paper also models the temperature decay of the extrinsic contribution as σ_ext(T)=σ_ext0/(aT+1)^2 due to electron-phonon scattering.","tokens_in":12249,"tokens_out":3558,"duration_ms":40393,"significance":"If the experimental claim is correct, this would be a rare direct observation of temperature-dependent intrinsic anomalous Hall conductivity arising from a magnetic transition, and it would be of interest to the condensed-matter community studying Berry-curvature engineering and kagome magnets. A clear strength is the independent DFT calculation: the computed evolution of σ_xy^A and σ_zx^A with the magnetization angle qualitatively supports the experimental scenario without being fitted to the transport data. However, the quantitative experimental evidence for the central claim rests entirely on two-block linear fits of the TYJ scaling relation, and the manuscript currently provides insufficient statistical detail and contains an internally inconsistent subtraction procedure. These issues must be resolved before the claim can be accepted.","major_comments":[{"comment":"The central claim that the intrinsic AHC is temperature dependent rests on the change of the fitted intercept b between two temperature blocks. The manuscript reports neither the slope (A in Eq. 5) nor the uncertainties for these fits, nor a statistical comparison of the two-block model against a single linear fit. Because the intercept is an extrapolation to σ_xx^2=0, a temperature-dependent slope within either block could produce a spurious intercept shift. Please provide the full fitting parameters, confidence intervals, and a goodness-of-fit comparison (e.g., an F-test) for the piecewise versus single-line model.","section":"Section III, Eq. (5), Figs. 3(b)-3(c)"},{"comment":"The extrinsic AHC is obtained by subtracting the low-temperature intercept b=112 S/cm from the total AHC at all temperatures, even though the high-temperature block fit gives b=170 S/cm. This choice is inconsistent and unsubstantiated; it biases the extracted σ_ext_xy and thereby the claimed (aT+1)^-2 temperature dependence. Please justify the subtraction or re-extract σ_ext_xy using the appropriate block-dependent intrinsic value.","section":"Section III, Fig. 3(d)"},{"comment":"The TYJ decomposition assumes a single linear relation σ_A = A σ_xx^2 + b valid over each temperature block, with b identified as the intrinsic contribution. Given that the spin reorientation is gradual, as shown in Figs. 2(a)-2(d), the coefficient A itself is expected to vary with temperature; the paper does not show that A is constant within each block or across the full range, and a temperature-dependent A would directly affect the inferred b values. Please address the sensitivity of the intercepts to the block choice (e.g., by moving the block boundary) and to a model with a temperature-dependent slope.","section":"Section III, Eq. (5)"}],"minor_comments":[{"comment":"The first term on the right-hand side, ρ_ext_xy0 σ_xx^2(T), mixes resistivity and conductivity notation; Fig. 3(d) and the text use σ_ext_xy0. Please clarify the notation and the units of the coefficient.","section":"Equation (5)"},{"comment":"The phrase 'some of all three contributions' should be 'sum of all three contributions'.","section":"Section III, before Eq. (4)"},{"comment":"The data points are shown without error bars; given that the intercepts are central to the claim, please include error estimates from the fits.","section":"Figs. 3(b)-3(c)"},{"comment":"The sentence beginning 'In this paper, the kagome lattice...' is grammatically incomplete; 'In this paper' appears to be a leftover from editing and should be removed or the sentence restructured.","section":"Introduction"}],"recommendation":"major_revision","confidential_remarks":"The DFT part is a genuine strength and provides an independent, qualitative check of the spin-reorientation scenario. The experimental analysis, however, is not yet convincing: the two-block TYJ fits and the inconsistent subtraction of b=112 S/cm need to be addressed with proper statistical treatment and robustness checks. If the authors can provide the missing fitting parameters and demonstrate that the intercept shift is not an artifact of the chosen block boundaries, the paper would be a valuable contribution. The topic fits the journal's scope, but the central quantitative claim currently rests on an analysis that is under-specified."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The core idea is good: use Fe3Ge's known spin-reorientation to test whether the intrinsic anomalous Hall conductivity changes when the easy axis rotates. That is worth doing, and the angle-dependent DFT is a genuine addition—they compute AHC for magnetization along 0°, 45°, and 90° and show the in-plane vs out-of-plane components swap dominance, matching the direction of the experimental change. That is real evidence and I don't think it appears in the prior Fe3Ge work they cite.\n\nThe experimental side is respectable: crystals seem fine, resistivity and magnetization match earlier reports, and TSR at 340 K is clearly identified. The TYJ analysis follows standard practice. But the central quantitative claim—b changes from 170 to 112 S/cm in-plane and 111 to 320 S/cm out-of-plane—is exactly as fragile as the stress-test says. The fits are two-block straight lines with no reported slopes, no confidence intervals, and no statistical test against a single line. The block split near 200 K is not tied to TSR, so it looks post hoc. And the extraction of the extrinsic in-plane AHC subtracts b = 112 S/cm at all temperatures even though their own high-temperature fit gives b = 170 S/cm. The text says the intrinsic conductivity for sigma_xy does not change much, which contradicts their own two-block result. That inconsistency needs to be fixed.\n\nThe supplementary plot of rho^A/M_s vs rho^2 does not rescue the claim, because it relies on the same two-block assumption. So all experimental support for the headline phenomenon reduces to those intercepts.\n\nOn the other hand, the DFT is independent and not fitted to transport. The angle-dependent crossover is qualitative but suggestive, and the calculated band-structure evolution with magnetization direction is a useful addition. The paper does not report absolute AHC values at EF for all angles with the same conditions, but Figures 4(c)-(g) give the relevant trends.\n\nBottom line: this is worth publishing as a study of anisotropic AHE and a proposed spin-reorientation mechanism, but the \"rare phenomenon\" claim outruns the current analysis. A serious referee should ask for a continuous temperature-resolved TYJ decomposition with uncertainties, a consistent subtraction procedure, and deposition of the underlying transport data. My own verdict is conditional: the qualitative story is plausible, but the quantitative case is not yet made.","headline":"A worthwhile spin-reorientation AHE study with genuinely new angle-dependent DFT, but the experimental case for temperature-dependent intrinsic AHC rests on fragile two-block TYJ fits that need error bars and a consistent subtraction.","tokens_in":12844,"tokens_out":1850,"would_cite":false,"duration_ms":23846,"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":"The paper argues that cooling Fe3Ge rotates its easy magnetization axis, which makes the Berry-curvature part of the Hall conductivity temperature-dependent.","keywords":["anomalous Hall effect","Berry curvature","spin reorientation","kagome lattice","Fe3Ge","skew scattering","electron-phonon scattering","topological metal"],"falsifier":"Repeat the scaling analysis on a Fe$_3$Ge crystal whose magnetization is pinned by a strong magnetic field so that the easy axis cannot rotate as temperature is swept through the spin-reorientation transition; if the fitted intrinsic intercept changes anyway, the central claim is wrong.","tokens_in":11816,"feed_emoji":"🧲","tokens_out":12760,"duration_ms":128932,"temperature":0.7,"pith_summary":"This paper argues that the intrinsic anomalous Hall conductivity of Fe$_3$Ge is temperature-dependent, a rarity because the intrinsic, Berry-curvature part of the anomalous Hall effect is normally fixed by the band structure. The driver is a spin-reorientation transition: below about 340 K the easy magnetization axis gradually cants from the out-of-plane direction toward the in-plane direction, and that canting changes the momentum-space Berry curvature. The experimental evidence comes from the TYJ scaling analysis, in which the fitted intrinsic intercept changes from 170 to 112 S/cm in-plane and from 111 to 320 S/cm out-of-plane as the temperature crosses the transition. First-principles calculations with the magnetization angle as a parameter reproduce the qualitative crossover, so the paper concludes that spin reorientation provides a practical knob for tuning Berry-curvature transport. If true, this makes Fe$_3$Ge a concrete case where a normally fixed intrinsic Hall term is controlled by temperature through magnetism.","feed_headline":"Cooling rotates Fe3Ge's easy axis, changing its intrinsic Hall effect","feed_subtitle":"A spin-reorientation transition near 340 K turns the Berry-curvature Hall term into a temperature-dependent quantity.","key_machinery":"The workhorse is the TYJ scaling law, an empirical relation that expresses the anomalous Hall conductivity as a slope term proportional to the square of the longitudinal conductivity plus a temperature-dependent intercept $b(T)$; the intercept is what the paper counts as the intrinsic, Berry-curvature contribution. The physical driver is the spin-reorientation transition at about 340 K, where magnetization data show the Fe moments canting from the $z$-axis toward the $xy$-plane as temperature falls. The band-structure calculations supply the link between the two: for magnetization angles $\\Theta = 0^\\circ$, $45^\\circ$, and $90^\\circ$, spin-orbit coupling gaps at Weyl and Dirac points change with $\\Theta$, which redistributes the integrated Berry curvature between in-plane and out-of-plane Hall conductivities and matches the experimental crossover.","core_discovery":"The central claim is that the intrinsic anomalous Hall conductivity of Fe$_3$Ge is not a fixed band-structure property but changes with temperature because the easy magnetization axis rotates. In the TYJ scaling law, $$-\\sigma_{xy}^{A}(T)=\\rho_{xy0}^{\\mathrm{ext}}\\sigma_{xx}^{2}(T)+b(T),$$ the intercept $b(T)$ is read as the intrinsic Hall contribution; the paper reports $b$ moving from 170 to 112 S/cm in-plane and from 111 to 320 S/cm out-of-plane between the high- and low-temperature regions. The remaining Hall signal is identified as extrinsic skew scattering, whose temperature decay is fit by $\\sigma_{xy}^{\\mathrm{ext}}(T)=\\sigma_{xy0}^{\\mathrm{ext}}/(aT+1)^2$ via electron-phonon scattering. Density functional theory calculations with the magnetization angle set to $0^\\circ$, $45^\\circ$, and $90^\\circ$ reproduce the qualitative crossover in which in-plane intrinsic anomalous Hall conductivity dominates above the spin-reorientation transition and out-of-plane intrinsic anomalous Hall conductivity dominates below it.","pith_inferences":["Inference: applying the same two-block scaling analysis at intermediate temperatures should show the intrinsic intercept moving continuously between the high- and low-temperature values, tracking the gradual canting angle; finer temperature windows would test this directly.","Inference: if the mechanism is easy-axis rotation rather than thermal smearing, a Fe$_3$Ge crystal pinned by a magnetic field so that the easy axis cannot rotate should show a nearly temperature-independent intrinsic intercept across the spin-reorientation region.","Inference: other ferromagnets with spin-reorientation transitions and nearby Weyl or Dirac nodes should show analogous temperature dependence in the intrinsic anomalous Hall conductivity, so reanalyzing existing AHE data across such transitions could reveal the same effect.","Inference: because the calculated Dirac-node gap depends on magnetization angle, angle-resolved photoemission across the spin-reorientation region could observe the gap opening and closing, giving a band-structure-level check of the Berry-curvature redistribution."],"forward_implications":["In Fe$_3$Ge the intrinsic anomalous Hall conductivity is not a fixed constant: rotating the easy axis from out-of-plane to in-plane changes the fitted intrinsic intercept from 170 to 112 S/cm in-plane and from 111 to 320 S/cm out-of-plane.","The sharp rise in total anomalous Hall conductivity below about 200 K is dominated by extrinsic skew scattering, while the rise above 200 K comes from the high-temperature intrinsic contribution.","The extrinsic skew-scattering contribution decays as $\\sigma_{xy}^{\\mathrm{ext}}(T)=\\sigma_{xy0}^{\\mathrm{ext}}/(aT+1)^2$, a temperature dependence set by electron-phonon scattering.","The crossover in which current direction has the larger intrinsic Hall conductivity is reproduced qualitatively by density functional theory as the magnetization angle is varied, indicating that the spin-reorientation transition itself is the control parameter.","The result gives an experimental route to Berry-curvature engineering in kagome ferromagnets: choose a material with a spin-reorientation transition, and cool it to select the intrinsic Hall response."],"supporting_citations":[{"why":"Supplies the TYJ scaling law used to separate intrinsic (intercept) from extrinsic (slope) anomalous Hall conductivity.","marker":"[37]"},{"why":"Documents the out-of-plane to in-plane spin reorientation in Fe3Ge below the transition.","marker":"[22]"},{"why":"Characterizes the magnetocrystalline anisotropy of Fe3Ge single crystals that drives the easy-axis rotation.","marker":"[24]"},{"why":"Shows spin reorientation alters the Dirac fermions and electronic structure in Fe3Ge, the microscopic route to changed Berry curvature.","marker":"[26]"},{"why":"Provides the electron-phonon scattering model used to fit the temperature decay of the extrinsic skew-scattering contribution.","marker":"[42]"},{"why":"Earlier study of electron-phonon scattering effects on the anomalous Hall conductivity of a kagome ferromagnet, the template for the extrinsic contribution analysis.","marker":"[21]"},{"why":"Prior demonstration that the intrinsic anomalous Hall effect can be temperature-dependent, the phenomenon here observed via spin reorientation.","marker":"[9]"}],"fun_headline_variants":["Fe3Ge spin reorientation tunes intrinsic Hall term","Temperature flips Fe3Ge easy axis, altering anomalous Hall","Berry curvature Hall effect varies with spin-axis tilt in Fe3Ge","Easy-axis rotation makes Fe3Ge's intrinsic Hall temperature-dependent"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The quantitative case rests on the assumption that the scaling-law plots can be split into two straight-line blocks with a constant intrinsic intercept inside each block, so the change in the fitted intercept is the only carrier of the temperature dependence.","fun_headline_variants_meta":{"raw":{"variants":["Fe3Ge spin reorientation tunes intrinsic Hall term","Temperature flips Fe3Ge easy axis, altering anomalous Hall","Berry curvature Hall effect varies with spin-axis tilt in Fe3Ge","Easy-axis rotation makes Fe3Ge's intrinsic Hall temperature-dependent"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000176,"raw_usage":{"total_tokens":1280,"prompt_tokens":929,"completion_tokens":351,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":545,"completion_tokens_details":{"reasoning_tokens":281}},"tokens_in":545,"tokens_out":351,"duration_ms":3761,"temperature":1.0,"reasoning_tokens":281,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-06T16:39:07.811320+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Repeat the scaling analysis on a Fe$_3$Ge crystal whose magnetization is pinned by a strong magnetic field so that the easy axis cannot rotate as temperature is swept through the spin-reorientation transition; if the fitted intrinsic intercept changes anyway, the central claim is wrong.","supporting_citations":[{"cited_title":"Neubauer, C","cited_arxiv_id":null,"evidence_quote":"Supplies the TYJ scaling law used to separate intrinsic (intercept) from extrinsic (slope) anomalous Hall conductivity."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Documents the out-of-plane to in-plane spin reorientation in Fe3Ge below the transition."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Characterizes the magnetocrystalline anisotropy of Fe3Ge single crystals that drives the easy-axis rotation."},{"cited_title":"Large topological Hall effect arising from spin reorientation in kagome magnet Fe3Ge","cited_arxiv_id":"2403.17354","evidence_quote":"Shows spin reorientation alters the Dirac fermions and electronic structure in Fe3Ge, the microscopic route to changed Berry curvature."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Earlier study of electron-phonon scattering effects on the anomalous Hall conductivity of a kagome ferromagnet, the template for the extrinsic contribution analysis."}],"review_version":1}