{"id":"46ee02bc-9ace-4736-9947-b50d288c8e17","arxiv_id":"2608.07052","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"For Co2MnSi Heusler films, the magneto-optical Kerr spectrum predicts the best Brillouin light scattering wavelength, with blue light much stronger than green.","lead":"Co2Mn-based magnetic films show very different light-reflecting Kerr signals depending on their chemical composition and laser color. The study shows that for Co2MnSi, reading the Kerr spectrum can predict the best laser color for Brillouin light scattering, turning a routine optics check into a guide for magnonics experiments.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"BLS wavelength comparison at different wavevectors confounds the claimed MOKE tracking; matched-k measurements are needed.","rationale":"The paper's stated goal is to show that MOKE spectroscopy can directly guide BLS probe wavelength selection, with the linchpin observation being the wavelength-dependent reversal of Co2MnSi's relative BLS intensity. The authors are transparent about many limitations: they separate linear and quadratic MOKE, reproduce Silber's spectra with scaling factors, state the cross-wavelength normalisation caveat, and discuss QMOKE effects. The data are archived and the analytical link to Hamrle et al. is reasonable. However, the key experiment does not control for the scattering wavevector: at 457 nm, φ = 2.5°; at 532 nm, φ = 10°, so the probed k changes by a factor of 3.4. Thermal magnon occupation and the dynamic matrix element depend on k and on the material's M_eff and exchange stiffness; Table 1 lists M_eff values from 835 to 1049 kA/m and thicknesses from 17 to 25 nm, so these magnonic factors are not sample-independent. A change in Co2MnSi's ranking between the two wavelengths could therefore arise from the different wavevector rather than from the wavelength dependence of |Φ_MOKE|². The paper's own footnote that absolute amplitudes at the two wavelengths cannot be compared makes this especially acute: the only cross-wavelength comparison used for the headline conclusion is exactly this one. A matched-k BLS measurement on the same film, with a spectral calibration against a reference sample, would settle the issue. The reader's concern about the transferability of the Silber et al. reference spectra is valid and complementary, but it is not the most load-bearing issue because even a perfect reference transfer would leave the wavevector confound in place.","tokens_in":14243,"tokens_out":11677,"duration_ms":107459,"concrete_test":"Measure BLS on the same Co2MnSi film at λ = 457 nm and λ = 532 nm with matched in-plane wavevector, e.g. keep φ457 = 2.5° and set φ532 = arcsin((λ532/λ457) sin 2.5°) ≈ 2.9°, calibrating laser power and detector response against a reference sample whose Kerr spectrum is known to be flat. If the ratio I_457/I_532 reproduces the ratio |Φ_MOKE(457)|²/|Φ_MOKE(532)|² from the own or reference MOKE spectra, the MOKE-tracking claim survives; if the ranking reverses or the ratio is flat, the original observation is dominated by the wavevector change rather than by the Kerr angle.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central demonstration—Co2MnSi is weakest at 532 nm but among the strongest at 457 nm, 'tracking the spectral dependence of its Kerr angle'—uses BLS data taken under different scattering conditions. In §2.3 and Fig. 4b, φ457 = 2.5° and φ532 = 10°, so the probed in-plane wavevector k∥ = (4π/λ) sinφ is 1.2×10^6 m^-1 at 457 nm and 4.1×10^6 m^-1 at 532 nm, a factor of 3.4. Thermal BLS intensity is not simply I_BLS ∼ |Φ_MOKE|² as Eq. (3) states; it also carries a thermal magnon occupation factor n(ω(k))+1 and a dynamical matrix element that depend on k and on material parameters (M_eff, exchange stiffness, thickness) which vary across the series (Table 1). The paper explicitly warns that normalised intensities 'must not be compared across the two wavelengths' (footnote in §3.3), yet the main conclusion is a cross-wavelength comparison of Co2MnSi's ranking. Without matching k, the observed ranking change cannot be uniquely attributed to the magneto-optical Kerr angle. The reference-spectra transferability concern is secondary: even a perfectly transferred Silber spectrum would not remove this wavevector confound.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports a combined magneto-optical Kerr effect (MOKE) spectroscopy and Brillouin light scattering (BLS) study of epitaxial Co2MnX Heusler films (X = Al, AlSi, Si, GaGe, Ge, Sn). MOKE spectroscopy from 550 to 900 nm shows that Co2MnSi has a strongly dispersive linear Kerr rotation and a significant quadratic MOKE (QMOKE) contribution, whereas Co2MnAl has an almost wavelength-independent linear response and negligible QMOKE. BLS measurements of thermal magnons at 532 nm and 457 nm show that Co2MnSi gives the weakest signal at 532 nm but among the strongest at 457 nm. The authors argue this ranking change tracks the spectral dependence of the Kerr angle, thereby demonstrating that MOKE spectroscopy can guide the choice of BLS probing wavelength. They also report a clustering of 532-nm BLS intensities by valence-electron count and discuss implications of QMOKE for nonlinear magnonics.","tokens_in":14485,"tokens_out":4955,"duration_ms":44713,"significance":"If the central correlation is established, the result is practically useful: it offers a simple spectroscopic criterion for selecting BLS wavelengths on Co2Mn-based Heusler films, and it provides an experimental test of the analytical MOKE-BLS intensity link. The manuscript benefits from a well-characterised sample series inherited from earlier detailed studies, transparent use of an external analytical formula (Ref. 18), and deposition of raw data in Zenodo. The symmetry-based separation of linear and quadratic MOKE is clearly described and does not involve circular fitting. The significance is currently conditional, because the key cross-wavelength BLS comparison is confounded by a wavevector mismatch and the blue-side interpretation relies on rescaled literature spectra rather than on measurements of the present films.","major_comments":[{"comment":"The central comparison of Co2MnSi's BLS ranking at 457 nm and 532 nm is made at different in-plane wavevectors k_∥ = (4π/λ) sin φ. With φ457 = 2.5° and φ532 = 10°, k_∥(457 nm) = 1.2×10^6 m^-1 while k_∥(532 nm) = 4.1×10^6 m^-1, a factor of 3.4. Thermal BLS intensity is not simply proportional to |Φ_MOKE|^2 as stated in Eq. (3): it also contains the thermal occupation factor n(ω(k)) + 1 and a k-dependent dynamical matrix element that depends on film thickness, effective magnetisation, exchange stiffness, and mode profile, all of which vary across the series (Table 1). The footnote in §3.3 correctly states that normalised amplitudes must not be compared across the two wavelengths, yet the paper's main conclusion—Co2MnSi 'recovers' from weakest at 532 nm to among the strongest at 457 nm—is exactly such a cross-wavelength comparison of relative ranking. Without matched-k data or a quantitative correction for these k-dependent factors, the ranking change cannot be uniquely attributed to the spectral dependence of the Kerr angle.","section":"§2.3 and Fig. 4b"},{"comment":"The blue-side recovery of Co2MnSi at 457 nm is not supported by the authors' own MOKE data, whose stated range is λ = 550–900 nm (Section 2.2). The 457 nm BLS point is therefore interpreted through the reference spectra of Silber et al., which were measured on a 30-nm film grown by a different method with different buffer and cap layers, and are brought into agreement by proportionality factors of −2 and 4 (Section 3.2). The 'tracking' of the Kerr angle in Fig. 4c is thus an inferred benchmark transfer rather than a direct measurement on the same sample series. Please either obtain MOKE data in the blue region for these films or explicitly present the blue-side agreement as a literature-based extrapolation, with a quantitative argument for transferability of the reference spectra to the present 17-nm films.","section":"§3.2, §3.3, Fig. 4c"},{"comment":"No error bars, confidence intervals, or numbers of averaged spectra are reported for the extracted BLS peak amplitudes, despite the text relying on comparative strength statements such as 'by far the weakest' and 'among the strongest'. These rank claims need uncertainty estimates to be falsifiable and to justify the cross-compound ordering at each wavelength. Without them, the statistical significance of the 457-nm recovery and the Boron/Carbon-group clustering cannot be assessed.","section":"§3.3 and Fig. 4b"}],"minor_comments":[{"comment":"The symmetry-based separation assumes 'negligible higher orders O(M^3)'; given that recent references report cubic-in-magnetisation MOKE in other cubic films, a brief justification of this assumption for Co2MnSi (for example, a field-dependence check of the even component) would strengthen the QMOKE assignment.","section":"§2.2"},{"comment":"The claim that 532-nm BLS intensities cluster by valence-electron count is based on seven samples without reported uncertainties. A scatter plot with per-sample variability or a small statistical test would make the clustering more convincing.","section":"§3.3"},{"comment":"The scaling factors −2 (for linMOKE) and 4 (for QMOKE) are attributed to double layer thickness and coordinate convention; the factor of 4 for the second-order term should be explained explicitly (e.g., as the square of the linear scaling), since the current text leaves this relationship implicit.","section":"§3.2 and Fig. 3"},{"comment":"There are several typographical and formatting issues: inconsistent spacing in compound names (e.g., 'Co 2MnXfilms'), the table header 'tCo2MnX' is not defined, and the footnote marker placement in §3.3 is distracting. A careful proofread is recommended.","section":"Throughout"}],"recommendation":"major_revision","confidential_remarks":null},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague, quick read of arXiv:2608.07052. What's new: a systematic comparison of linear and quadratic MOKE across the Co2MnX family, with clear evidence that only Co2MnSi shows significant QMOKE, and a first attempt to connect MOKE spectra to BLS intensity at two wavelengths. The MOKE data itself look solid, the reproduction of Silber's spectra with scaling factors is plausible, and the citation to Hamrle's analytical link is appropriate. The paper is honest about its own limitations, including the footnote that absolute BLS intensities cannot be compared across wavelengths and the caveat that the symmetry-based QMOKE separation cannot distinguish the two quadratic terms.\n\nThe soft spots are real but not fatal. First, the blue-side BLS result for Co2MnSi at 457 nm is compared to reference MOKE spectra rather than own measurements; the scaling factors of -2 and 4 are physically motivated, but this remains an inferred benchmark. Second, the two BLS wavelengths were measured at different incidence angles, φ457=2.5° and φ532=10°, giving a factor of ~3.4 difference in probed wavevector. The paper warns against cross-wavelength intensity comparisons, yet the key claim—that Co2MnSi's ranking flips from weakest to strongest—is exactly a cross-wavelength comparison. Thermal BLS intensity carries a wavevector-dependent occupation factor and dynamical matrix element, so the ranking change cannot be uniquely attributed to the Kerr angle. Matched-k BLS measurements would settle this, and the authors should either provide them or temper the claim.\n\nOther issues are minor: no error bars anywhere, and the family-wide statements about dominant linear response in Co2MnAl, Co2MnGa, and Co2MnSn rest on single-wavelength data for those compounds. That said, the paper is a good practical contribution for Heusler BLS users. It deserves a serious referee, but the referee should ask for matched-k BLS or a clearly softened conclusion about \"tracking the Kerr angle.\"","headline":"Useful MOKE data and a practical wavelength guide for BLS, but the central two-wavelength comparison is confounded by a wavevector mismatch that needs addressing.","tokens_in":15025,"tokens_out":3585,"would_cite":true,"duration_ms":33349,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["78.20.Ls","75.70.-i","78.35.+c"],"model":"deepseek-v4-flash","headline":"MOKE spectra predict the BLS signal strength across Co2Mn-based Heusler compounds, with Co2MnSi flipping from weakest to among the strongest when the probe moves from green to blue.","keywords":["Heusler compounds","Co2MnSi","magneto-optical Kerr effect","quadratic MOKE","Brillouin light scattering","magnonics","spin waves"],"falsifier":"Measure Kerr rotation and ellipticity spectra of the exact Co2MnSi films used in the BLS experiments down to 457 nm and compare the squared complex Kerr angle at 457 nm and 532 nm with the measured BLS intensity ranking; if the squared Kerr angle at 457 nm is not among the strongest (or does not rise relative to the 532 nm value), the claimed tracking of BLS by the Kerr spectrum fails.","tokens_in":14059,"feed_emoji":"💡","tokens_out":20004,"duration_ms":139507,"temperature":0.7,"pith_summary":"The paper aims to establish that the magneto-optical Kerr effect (MOKE) spectrum of a Heusler thin film can predict which probing wavelength will give a strong Brillouin light scattering (BLS) signal, because the BLS intensity is proportional to the squared complex Kerr angle. Across a series of epitaxial Co2MnX films (X = Al, Si, Ga, Ge, Sn and quaternaries), only Co2MnSi shows a strong, wavelength-dependent quadratic MOKE, with its Kerr rotation changing sign near 600 nm and its squared magnitude dipping around 550–620 nm before recovering toward the blue. In BLS measurements, Co2MnSi indeed gives the weakest signal at 532 nm but is among the strongest at 457 nm, matching its Kerr spectrum; the other compounds show a flatter response. The paper also reports that BLS intensities at 532 nm cluster by the valence-electron count of the X element, pointing to a band-filling origin. If correct, this work offers a simple table-top way to choose BLS laser wavelengths and experimentally confirms the analytical MOKE–BLS intensity link.","feed_headline":"MOKE spectra predict the best BLS probing wavelength for Heusler films","feed_subtitle":"Co2MnSi's weak 532 nm signal is among the strongest at 457 nm, tracking its Kerr angle.","key_machinery":"The central object is the relation $I_{\\mathrm{BLS}} \\sim |\\Phi_{\\mathrm{MOKE}}|^2 = \\theta_{\\mathrm{MOKE}}^2 + \\varepsilon_{\\mathrm{MOKE}}^2$ connecting the BLS intensity of a spin wave to the squared modulus of the complex Kerr angle (rotation $\\theta$ plus ellipticity $\\varepsilon$). The argument is carried by MOKE spectroscopy, which measures this complex angle, together with a symmetry-based separation of the measured Kerr loops into odd (linear, linMOKE) and even (quadratic, QMOKE) parts by comparing increasing and decreasing field branches. The wavelength dependence of the separated contributions, benchmarked against reference spectra from a thicker Co2MnSi film, then predicts the relative BLS intensity ranking between compounds and wavelengths.","core_discovery":"On the paper's own terms, the central discovery is that in Co2Mn-based Heusler films the BLS intensity tracks the squared complex Kerr angle, so the spectral shape of the MOKE response directly determines which probing wavelength gives a strong light-scattering signal. For Co2MnSi, the Kerr rotation is strongly dispersive across 550–900 nm, with a sign change near 600 nm, and the squared Kerr angle reaches a minimum around 550–620 nm before recovering at shorter wavelengths; the BLS measurements confirm this ranking by showing Co2MnSi as the weakest scatterer at 532 nm and among the strongest at 457 nm. The paper further finds that the quadratic magneto-optical Kerr effect (QMOKE) is significant and wavelength-dependent only in Co2MnSi among the ternary compounds, reaching up to ~150% of the total signal along the <100> axes, and that the linear contribution dominates in Co2MnAl, Co2MnGa and Co2MnSn. The authors interpret these results as an experimental confirmation of the analytical MOKE–BLS relation and as a guide for choosing BLS wavelengths in Heusler compounds.","pith_inferences":["The blue-side BLS comparison at 457 nm is not backed by the authors' own MOKE data, which stop at 550 nm; the claimed recovery rests on scaled reference spectra of a thicker, differently grown Co2MnSi film, so the central claim would be weakened if those spectra are not representative of the present 17 nm films.","The band-filling correlation observed at 532 nm suggests a testable extension: measuring the full MOKE spectrum of Co2MnSn could separate the influence of L21 ordering from the valence-electron count on the quadratic response, since Co2MnSn has mixed inverse/full Heusler order.","If the MOKE–BLS link is generic across materials, then BLS intensity calibration could be transferred between laboratories via simple MOKE spectra, which are easier to standardize and do not require a multistage interferometer.","The higher-harmonic mixing caution is directly testable: comparing BLS spectra of large-amplitude spin waves along <100> and <110> directions in Co2MnSi, where the quadratic MOKE differs strongly, would reveal whether higher harmonic content arises from magneto-optical artifacts rather than genuine spin-wave modes."],"forward_implications":["Choosing a blue probing wavelength (~457 nm) instead of the common green (532 nm) can strongly boost the BLS signal of Co2MnSi films, directly improving signal-to-noise in magnonic measurements.","MOKE spectroscopy can serve as a quick prescreen for the optimal BLS laser wavelength in other material families, replacing trial-and-error with a table-top measurement.","The valence-electron-count clustering of BLS intensities at 532 nm suggests that band-filling (Slater–Pauling) engineering could be used to design Heusler compositions with favorable magneto-optical response at a desired wavelength.","The large, wavelength-dependent QMOKE in Co2MnSi implies that BLS experiments along <100> directions or at wavelengths where QMOKE is strong may mix higher harmonic responses and create artifacts when probing large-amplitude driven spin waves.","The experimental confirmation of the MOKE–BLS link means that relative BLS intensities across compounds can be predicted from Kerr spectra, including the ellipticity contribution, within the same measurement conditions."],"supporting_citations":[{"why":"Supplies the reference MOKE spectra of Co2MnSi over 225–1550 nm, used to benchmark the Kerr rotation and to extend the wavelength comparison below 550 nm.","marker":"[14]"},{"why":"Gives the analytical relation connecting BLS intensity to the squared complex Kerr angle, the central link the paper tests experimentally.","marker":"[18]"},{"why":"Provides the numerical reference data for the Co2MnSi Kerr spectra used in the blue-side comparison and the squared-angle curves.","marker":"[38]"},{"why":"Supplies the sample series and their structural and magnetic parameters (thickness, magnetisation, ordering, spin polarisation, damping) for the Co2MnX films.","marker":"[17]"},{"why":"Reports the ultralow Gilbert damping and ordering of the Co2Mn-based Heusler films, anchoring the material characterization.","marker":"[26]"},{"why":"Establishes that the quadratic MOKE in Co2MnSi scales with L21 ordering, used to interpret the QMOKE strength observed here.","marker":"[35]"},{"why":"Provides the symmetry-based method for separating linear and quadratic MOKE contributions, applied here to extract linMOKE and QMOKE.","marker":"[22]"}],"fun_headline_variants":["MOKE spectra guide BLS wavelength choice in Heusler films","Co2MnSi's BLS signal flips from weak to strong across wavelengths","Kerr angle shape sets the best BLS probing window for Heuslers","For Co2MnSi, BLS strength follows Kerr angle's spectral swing","Heusler MOKE predicts which BLS wavelength lights up Co2MnSi"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that the reference MOKE spectra of a 30 nm magnetron-sputtered Co2MnSi film, scaled by factors of -2 and 4, accurately describe the wavelength dependence of the present 17 nm MBE-grown films below 550 nm, where the authors' own MOKE data are absent.","fun_headline_variants_meta":{"raw":{"variants":["MOKE spectra guide BLS wavelength choice in Heusler films","Co2MnSi's BLS signal flips from weak to strong across wavelengths","Kerr angle shape sets the best BLS probing window for Heuslers","For Co2MnSi, BLS strength follows Kerr angle's spectral swing","Heusler MOKE predicts which BLS wavelength lights up Co2MnSi"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000165,"raw_usage":{"total_tokens":1323,"prompt_tokens":1092,"completion_tokens":231,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":708,"completion_tokens_details":{"reasoning_tokens":128}},"tokens_in":708,"tokens_out":231,"duration_ms":2248,"temperature":1.0,"reasoning_tokens":128,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-10T15:41:12.503561+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure Kerr rotation and ellipticity spectra of the exact Co2MnSi films used in the BLS experiments down to 457 nm and compare the squared complex Kerr angle at 457 nm and 532 nm with the measured BLS intensity ranking; if the squared Kerr angle at 457 nm is not among the strongest (or does not rise relative to the 532 nm value), the claimed tracking of BLS by the Kerr spectrum fails.","supporting_citations":[{"cited_title":"Scaling of quadratic and linear magneto-optic Kerr effect spectra with L2 1 ordering of Co2MnSi Heusler compound,","cited_arxiv_id":null,"evidence_quote":"Supplies the reference MOKE spectra of Co2MnSi over 225–1550 nm, used to benchmark the Kerr rotation and to extend the wavelength comparison below 550 nm."},{"cited_title":"Analytical expression of the magneto-optical Kerr effect and Brillouin light scattering intensity arising from dynamic magnetization,","cited_arxiv_id":null,"evidence_quote":"Gives the analytical relation connecting BLS intensity to the squared complex Kerr angle, the central link the paper tests experimentally."},{"cited_title":"Silber et al.,Longitudinal and quadratic magnetooptic Kerr effect spectra of Co 2MnSi Heusler compound, Mar","cited_arxiv_id":null,"evidence_quote":"Provides the numerical reference data for the Co2MnSi Kerr spectra used in the blue-side comparison and the squared-angle curves."},{"cited_title":"Engineering Co 2MnAlxSi1-x Heusler Compounds as a Model System to Correlate Spin Polarization, Intrinsic Gilbert Damping, and Ultrafast Demagnetization,","cited_arxiv_id":null,"evidence_quote":"Supplies the sample series and their structural and magnetic parameters (thickness, magnetisation, ordering, spin polarisation, damping) for the Co2MnX films."},{"cited_title":"Quadratic magneto- optical Kerr effect in Co 2MnSi,","cited_arxiv_id":null,"evidence_quote":"Establishes that the quadratic MOKE in Co2MnSi scales with L21 ordering, used to interpret the QMOKE strength observed here."},{"cited_title":"Huge quadratic magneto-optical Kerr effect and magnetization reversal in the Co 2FeSi Heusler compound,","cited_arxiv_id":null,"evidence_quote":"Provides the symmetry-based method for separating linear and quadratic MOKE contributions, applied here to extract linMOKE and QMOKE."}],"review_version":1}