{"id":"fa094b6c-cf71-44c9-a06e-6b326bad54d7","arxiv_id":"2502.03166","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":1,"one_line_summary":"Thermal spin-wave noise measured with a single NV center reveals the sign of the interfacial DMI and distinguishes Neel from Bloch skyrmions.","lead":"This paper shows that thermal magnetic noise emitted by spin waves inside domain walls and skyrmions encodes the handedness of these magnetic textures, and that a diamond nitrogen-vacancy sensor can read it out. The sign of the Dzyaloshinskii-Moriya interaction and the Neel or Bloch nature of skyrmions can be inferred from the amplitude and angular distribution of this noise.","discovery_kind":"new_method","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Sign-of-DMI claim hinges on one uncontrolled null comparison; standoff and probe differences between Fig. 2 and Fig. 3 could explain the blank map.","rationale":"The paper's central claim has two parts: (1) noise amplitude encodes the sign of DMI, and (2) skyrmion contour structure reveals Néel/Bloch chirality. The skyrmion part is supported by an average over 19 objects compared with disorder-averaged micromagnetics, and the agreement with Néel over Bloch is a meaningful internal check. The sign-inference part, however, rests on a single comparison between two different samples and geometries. The reader identified this as the weakest assumption, and I agree. I considered other potential issues—such as the idealized straight-wall dispersion at small k, the Halbach analogy, or the thermal population argument—but these are either addressed by the wavevector filtering (which peaks near 1/d, not at small k) or are plausible extensions of known physics. The decisive weakness is empirical: the one data point that supposedly proves chirality-dependent noise is a null result obtained under changed conditions. The concrete test I propose is computational and uses the authors' own model, so it is feasible without new experiments. If the model predicts a detectable signal at dNV=72 nm for the reversed chirality, then the null result is meaningful; if not, the abstract's sign claim is overstated. The reader's CONDITIONAL verdict therefore remains appropriate; I would not move it to ACCEPT or REJECT based on this analysis, because the concern is addressable and the rest of the paper's evidence is solid.","tokens_in":9658,"tokens_out":7923,"duration_ms":84288,"concrete_test":"Use the same MuMax3/Ref-18 noise model to compute the expected wall noise contrast for the exact Fig. 3 geometry (SAF on 20 nm SiN membrane, dNV=72 nm, D=-0.62 mJ/m², including both Co layers) and compare with the detection floor estimated from the domain T1 scatter in Fig. 3(c)-(d). If the predicted PL drop is below the noise floor, the blank map is explained by standoff/probe differences and the DMI-sign inference is unsupported; if the predicted drop is above the floor, the null result strengthens the one-sided flux mechanism.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The abstract's strongest claim—that the sign of the DMI can be inferred from the amplitude of detected noise—is supported experimentally by exactly one comparison: a 10% PL drop above left-handed Néel walls at dNV=62 nm (Fig. 2) versus no detectable wall contrast above right-handed Néel walls at dNV=72 nm through a 20 nm SiN membrane (Fig. 3). These two measurements differ in probe, standoff, substrate, and measurement side. The relaxometry signal scales steeply with standoff, so the null result in Fig. 3 may reflect the larger dNV or membrane-related artifacts rather than the one-sided flux mechanism. The single-layer control mentioned in the text (Fig. S1) is not shown in the main text and is described as lower quality. Because the sign assignment depends on interpreting this null as the predicted suppression for the opposite chirality, the central claim is not yet secured. This is not an internal inconsistency; it is an uncontrolled confound in the decisive experiment. The Halbach mechanism itself is plausible, and the skyrmion contour statistics are internally supported, but the sign-inference leg of the paper requires a controlled two-sided or equal-standoff comparison.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper proposes that scanning NV-center relaxometry can probe the sign and strength of the interfacial Dzyaloshinskii-Moriya interaction (DMI) by detecting magnetic noise from thermally excited spin waves confined in domain walls and skyrmions. The mechanism combines two effects: the DMI-induced nonreciprocal spin-wave dispersion, which makes the wavevector population in a Néel wall asymmetric, and the one-sided stray field of the spin-wave helix (a Halbach-array-like configuration), which makes the noise detected above the film depend on the direction of the wavevector. The authors support the idea with micromagnetic noise calculations (Fig. 1) and two experiments on synthetic antiferromagnets: a strong relaxometry contrast above left-handed Néel walls (Fig. 2) and a blank noise map above right-handed walls measured through a SiN membrane (Fig. 3). They also analyze the noise distribution along the contour of skyrmions and find an angular modulation consistent with Néel rather than Bloch skyrmions (Fig. 4).","tokens_in":9776,"tokens_out":10897,"duration_ms":105579,"significance":"If the mechanism and the experimental validation are correct, this work offers a new, label-free approach to determine the chirality of magnetic textures and the sign of interfacial DMI, which could be particularly useful for low-moment systems such as ferrimagnets and antiferromagnets where existing techniques are difficult to apply. The theoretical idea is physically well motivated, and the numerical model is credible, using material parameters from prior work and including disorder in the skyrmion simulations. The skyrmion contour analysis, averaged over 19 objects, is a novel observation. The paper also makes a falsifiable prediction: the noise contrast should vanish or reverse when the wall chirality is reversed, a prediction that the authors attempt to test. However, the experimental support for the sign-inference claim is currently incomplete, as detailed below.","major_comments":[{"comment":"The central claim that the noise amplitude encodes the sign of D is supported by only one comparison, between Fig. 2 and Fig. 3, and those two measurements differ in several control parameters: standoff (62 vs 72 nm), diamond probe, substrate (Si/SiO2 vs SiN membrane), and measurement side (top vs through the membrane). Because the relaxometry signal depends on the filter function ke^{-2kdNV}, and because the membrane can introduce scattering or stress artifacts, the null result in Fig. 3 does not uniquely establish the predicted suppression for the opposite chirality. The single-layer control with identical probe and dNV is only mentioned in the text as Fig. S1 and is described as lower quality. To secure the sign-inference claim, the authors should present the controlled equal-standoff comparison in the main text with a statistical analysis of the null, or provide a quantitative calculation of the expected noise at dNV = 72 nm showing that the mechanism would still be detectable if present.","section":"Main text, Figs. 2 and 3"},{"comment":"The conclusion that skyrmion noise maps give 'insight into the strength of DMI involved in their stabilization' is not supported by the presented data. The measured observable is the normalized PL decrease along the skyrmion contour; the simulations in Fig. 4 show that left- and right-handed Néel skyrmions have the same angular profile (maximum at φ = 0) and differ only in the overall noise amplitude. Without an absolute calibration relating the PL decrease to the noise power, the experiment cannot distinguish left from right chirality, and therefore cannot provide quantitative information on the DMI strength. The text should either restrict the claim to distinguishing Néel from Bloch character, or provide a quantitative amplitude calibration and a comparison with the simulated absolute noise levels.","section":"Main text, section 'Going a step further', Fig. 4"},{"comment":"The phrase 'the sign of the DMI can be inferred from the amplitude of the detected noise' overstates the current evidence. In both experimental samples the DMI sign was already known from prior work (Ref. 40), and the measurement confirms the expected correlation rather than demonstrating inference on an unknown sample. Given the confounds identified in the Fig. 2/Fig. 3 comparison, the wording should be revised to present this as a proof-of-principle demonstration on samples with known DMI sign, or a blind test on a sample of unknown sign should be added.","section":"Abstract and Conclusion"}],"minor_comments":[{"comment":"The name 'Dzyaloshinskii' is misspelled as 'Dzyaloshinkii' in the title, the abstract, and the main text; it should be corrected throughout.","section":"Title and Abstract"},{"comment":"The caption contains typographical errors: '(b) Stray field map measured simultaneously with (b)' should refer to panel (a), and the phrases '(c)-(d) Relaxation time curves measured above a domain (b) or above a domain wall (c)' use the wrong panel labels.","section":"Fig. 3 caption"},{"comment":"The statement 'No data is shown for small k in the domain wall because a perfectly straight wall is unstable under these conditions' is unclear; the authors should briefly explain how this truncation affects the computed noise levels, since the noise integral may depend on the excluded modes.","section":"Fig. 1(c)"},{"comment":"The filter function ke^{-2kdNV}(1-e^{-2kt}) is introduced without defining t; the film thickness should be defined at first use to avoid ambiguity.","section":"Text near Eq. (1) (k-filter function)"},{"comment":"The paragraph introducing the SAF stack (Fig. 2a) states that the wall is expected to be left-handed Néel because of the Pt/Co DMI, but it does not explain how the two Co layers in the synthetic antiferromagnet contribute to the net DMI; a brief clarification would improve readability.","section":"Experimental sample description"}],"recommendation":"major_revision","confidential_remarks":"The paper is a good fit for the journal and the central physical idea is attractive. The main obstacle is the experimental validation of the sign-inference claim, which currently rests on an uncontrolled comparison between two different sample geometries. If the authors can provide the controlled single-layer data in the main text (or an equivalent equal-standoff comparison) with proper error analysis, the paper would be suitable for publication. I would also encourage them to temper the 'strength of DMI' statement in the skyrmion section unless a quantitative amplitude calibration is supplied."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague,\n\nThis paper does something new: thermal spin-wave noise measured with NV relaxometry is used to infer the sign of the interfacial DMI and to distinguish Néel from Bloch skyrmions. The mechanism is coherent: DMI makes wall-confined spin-wave dispersion nonreciprocal, and the Halbach-like one-sided stray field means the NV sees this noise mainly from one side of the film. The micromagnetics model is standard, and the skyrmion contour statistics over 19 objects match the Néel-left prediction and not the Bloch pattern. That part is the strongest evidence in the paper.\n\nThe soft spot is exactly what the stress-test note flags. The experimental proof that noise amplitude reverses with DMI sign is a single comparison: a 10 percent PL drop above left-handed Néel walls at dNV = 62 nm versus a blank map above right-handed Néel walls at dNV = 72 nm through a 20 nm SiN membrane. Those differ in probe, standoff, substrate, and measurement side. Since relaxometry signal scales steeply with standoff, the null could reflect the geometry rather than the one-sided flux mechanism. The paper mentions a single-layer control with identical probe and dNV for both chiralities, but that is in the supplementary and described as lower quality. So the abstract's sign-inference claim is not yet secured by main-text data. This is an uncontrolled confound in the decisive experiment, not an internal contradiction. The fix is an equal-standoff, same-probe comparison or a two-sided measurement.\n\nOther soft spots are minor. DMI strength is taken from prior work, and the paper itself notes the straight-wall dispersion breaks down at small k. The skyrmion angle-resolved data avoids the null-interpretation problem and independently supports the handedness picture, so the paper does not rest entirely on the weak leg.\n\nWho should read this: people working on NV relaxometry, chiral magnetism, and DMI characterization. It is a useful qualitative complement to BLS and spin-orbit torque methods, especially for low-stray-field samples. I would send it to a serious referee. The modeling is defensible and the method is promising, but I would not cite it as establishing the effect until the sign-inference leg is controlled.\n\nBest","headline":"NV relaxometry spin-wave noise is a genuinely new DMI-sign probe, but the sign leg currently rests on one uncontrolled null comparison; worth refereeing.","tokens_in":10453,"tokens_out":2513,"would_cite":false,"duration_ms":21866,"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 claims that the amplitude of thermal spin-wave noise from domain walls and skyrmions, read by a single NV center, encodes the sign and handedness of the interfacial Dzyaloshinskii-Moriya interaction.","keywords":["nitrogen-vacancy center relaxometry","Dzyaloshinskii-Moriya interaction","thermal spin-wave noise","domain walls","skyrmions","magnetic chirality","nonreciprocal spin waves","synthetic antiferromagnets"],"falsifier":"Measure the NV relaxometry signal above the same domain wall from both sides of the film, using probes with the same standoff distance; if the wall that appears noisy from one side also appears noisy from the other, or if the predicted handedness contrast is reversed for a sample whose DMI sign is independently known from Brillouin light scattering, the central claim would be contradicted.","tokens_in":9388,"feed_emoji":"🧲","tokens_out":5929,"duration_ms":53021,"temperature":0.7,"pith_summary":"This paper tries to establish that the handedness of chiral magnetic textures can be read directly from the amplitude of thermal spin-wave noise measured with a scanning nitrogen-vacancy (NV) center. The authors argue that in a perpendicularly magnetized film, spin waves trapped inside a domain wall have a DMI-split, nonreciprocal dispersion, and that the stray field they produce is pushed preferentially to one side of the film, like the one-sided flux of a Halbach array. Because the NV center filters the noise by frequency and by wavevector, the detected noise level above a wall depends on which wavevector direction is thermally populated, and that depends on the sign of the DMI. They support the claim with numerical noise maps and with relaxometry measurements on synthetic antiferromagnets, where left-handed Néel walls give a clear noise signal and right-handed walls give almost none. They further show that the angular distribution of noise around skyrmion contours reveals their Néel or Bloch character.","feed_headline":"Thermal spin-wave noise reveals DMI sign in one scan","feed_subtitle":"A single NV relaxometry map tells left- from right-handed domain walls and skyrmion chirality.","key_machinery":"The load-bearing machinery is the combination of nonreciprocal spin-wave dispersion inside chiral textures and wavevector-dependent one-sided stray fields. Inside a Néel domain wall the dispersion satisfies $\\omega(k) \\neq \\omega(-k)$ because DMI and dipolar interactions break inversion symmetry; at the NV's frequency filter this makes the thermal occupation $n(k) \\simeq k_B T/\\hbar\\omega(k)$ unequal for opposite $k$. The stray field of a wall-confined spin wave is the magnetic analogue of a Halbach array: in-plane and out-of-plane contributions cancel on one side of the film and reinforce on the other, so which side radiates depends on the sign of $k$ and on the wall chirality. The NV center acts as a double filter, frequency-selective near its zero-field resonance and wavevector-selective through the kernel $k e^{-2 k d_{\\mathrm{NV}}} (1 - e^{-2 k t})$, so the detected relaxation rate is dominated by one propagation direction set by the sign of $D$.","core_discovery":"On its own terms, the paper's central discovery is a qualitative variant of spin-wave DMI metrology: the sign of the interfacial Dzyaloshinskii-Moriya interaction can be inferred from the amplitude of magnetic noise emitted by confined thermal spin waves and detected by an NV center, without needing to resolve the spin-wave dispersion directly. For a 180° Néel wall, the DMI makes the dispersion nonreciprocal, so modes with opposite wavevector have different thermal populations; simultaneously, the wall's in-plane magnetization fluctuations generate a stray field that is one-sided, with the dominant side set by the wavevector direction and wall chirality. The NV's frequency filtering near 2.87 GHz and wavevector filtering at roughly $1/d_{\\mathrm{NV}}$ select one branch, and the resulting $T_1$ shortening, seen as a photoluminescence drop, is therefore stronger for one wall handedness. The same mechanism makes the noise around a skyrmion contour nonuniform, with an angular pattern that depends on whether the boundary is Néel or Bloch and on the chirality; measured contours on synthetic antiferromagnet skyrmions match the Néel-left prediction, while Bloch predictions differ qualitatively.","pith_inferences":["Inference: if the wall-versus-domain noise contrast is calibrated against a sample with known D, the same relaxometry measurement could yield a quantitative D value, not just its sign, by matching the measured ratio to simulated curves such as the D-dependence shown in Fig. 1(d).","Inference: the one-sided-flux mechanism predicts a mirror asymmetry, so reversing the sensing side of the film should swap which wall handedness appears noisy; this can be tested on the same stack with two probes or after flipping the sample.","Inference: the angular noise pattern around a single skyrmion might map local DMI inhomogeneity, since variations in D should show up as variations in contour contrast around one skyrmion.","Inference: the method could be applied to chiral domain walls in ferrimagnets near compensation, where small stray fields and gigahertz dynamics make other probes difficult."],"forward_implications":["A single scanning relaxometry map can identify the sign of the interfacial DMI in a sample with domain walls, rather than requiring Brillouin light scattering or spin-orbit-torque measurements.","The angular modulation of noise around skyrmion contours distinguishes Néel from Bloch skyrmions and can indicate their chirality, which is otherwise only accessible through quantitative stray-field imaging.","The method extends naturally to low-stray-field systems such as synthetic antiferromagnets, ferrimagnets, and antiferromagnets, where small static fields do not disturb the NV center's spin-state mixing.","Because the signal depends on the nonreciprocal occupation of confined spin-wave modes, it provides a way to probe spin waves in nanoscale textures that are difficult to address with conventional magnonic techniques."],"supporting_citations":[{"why":"Supplies the mechanism that a propagating spin wave's stray field is one-sided, the Halbach-array analogy on which the wall-noise asymmetry rests.","marker":"[37]"},{"why":"Establishes the scanning NV relaxometry method for non-collinear magnetic textures and the T1-shortening contrast above domain walls that this work extends to chiral walls.","marker":"[18]"},{"why":"Defines the existing quantitative DMI measurement techniques that this qualitative noise variant extends.","marker":"[25]"},{"why":"Provides the domain-wall magnonic waveguide picture and the wall-confined spin-wave dispersion used in the model.","marker":"[26]"},{"why":"Shows unidirectional spin-wave channeling along walls, supporting the nonreciprocal wall modes at the core of the argument.","marker":"[27]"},{"why":"Defines one-sided flux configurations (Halbach arrays), the stray-field analogy used to explain side-dependent noise.","marker":"[38]"},{"why":"Supplies the synthetic-antiferromagnet multilayer, skyrmion nucleation protocol, and the independently measured DMI value used to identify wall handedness.","marker":"[40]"},{"why":"Relates the NV photoluminescence drop to magnetic noise through the quantitative T1 response, the transduction used in all maps.","marker":"[29]"}],"fun_headline_variants":["NV relaxometry samples thermal spin-wave noise to reveal DMI sign","Thermal spin-wave noise in one NV scan exposes DMI handedness","Skyrmion and domain-wall noise maps DMI sign via NV relaxometry","A single NV map: thermal spin-wave noise tells DMI chirality"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The whole contrast mechanism rests on the assumption that spin waves confined in a Néel wall radiate a one-sided stray field whose dominant side is locked to the wavevector direction and wall chirality, and that the blank noise map seen through the membrane is caused by that one-sided flux rather than by the larger standoff, a different probe, or sample artifacts.","fun_headline_variants_meta":{"raw":{"variants":["NV relaxometry samples thermal spin-wave noise to reveal DMI sign","Thermal spin-wave noise in one NV scan exposes DMI handedness","Skyrmion and domain-wall noise maps DMI sign via NV relaxometry","A single NV map: thermal spin-wave noise tells DMI chirality"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000347,"raw_usage":{"total_tokens":1919,"prompt_tokens":984,"completion_tokens":935,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":600,"completion_tokens_details":{"reasoning_tokens":856}},"tokens_in":600,"tokens_out":935,"duration_ms":8750,"temperature":1.0,"reasoning_tokens":856,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-09T05:40:13.926519+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the NV relaxometry signal above the same domain wall from both sides of the film, using probes with the same standoff distance; if the wall that appears noisy from one side also appears noisy from the other, or if the predicted handedness contrast is reversed for a sample whose DMI sign is independently known from Brillouin light scattering, the central claim would be contradicted.","supporting_citations":[{"cited_title":"Devolder, Propagating-spin-wave spectroscopy using inductive antennas: Conditions for unidirectional energy flow, Physical Review Applied 20, 054057 (2023)","cited_arxiv_id":null,"evidence_quote":"Supplies the mechanism that a propagating spin wave's stray field is one-sided, the Halbach-array analogy on which the wall-noise asymmetry rests."},{"cited_title":"Finco, A","cited_arxiv_id":null,"evidence_quote":"Establishes the scanning NV relaxometry method for non-collinear magnetic textures and the T1-shortening contrast above domain walls that this work extends to chiral walls."},{"cited_title":"Kuepferling, A","cited_arxiv_id":null,"evidence_quote":"Defines the existing quantitative DMI measurement techniques that this qualitative noise variant extends."},{"cited_title":"Garcia-Sanchez, P","cited_arxiv_id":null,"evidence_quote":"Provides the domain-wall magnonic waveguide picture and the wall-confined spin-wave dispersion used in the model."},{"cited_title":"Henry, D","cited_arxiv_id":null,"evidence_quote":"Shows unidirectional spin-wave channeling along walls, supporting the nonreciprocal wall modes at the core of the argument."},{"cited_title":"Mallinson, One-sided fluxes – A magnetic curiosity?, IEEE Transactions on Magnetics 9, 678 (1973)","cited_arxiv_id":null,"evidence_quote":"Defines one-sided flux configurations (Halbach arrays), the stray-field analogy used to explain side-dependent noise."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the synthetic-antiferromagnet multilayer, skyrmion nucleation protocol, and the independently measured DMI value used to identify wall handedness."},{"cited_title":"Rollo, A","cited_arxiv_id":null,"evidence_quote":"Relates the NV photoluminescence drop to magnetic noise through the quantitative T1 response, the transduction used in all maps."}],"review_version":1}