{"id":"2675202c-9da4-4ae7-8f67-ab5a47d52cc4","arxiv_id":"2411.14415","paper_version":1,"verdict":"ACCEPT","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":4,"one_line_summary":"Single-crystal neutron diffraction determines the ground-state magnetic structures of RV6Sn6 for R = Tb, Dy, Ho, Er: ferromagnetic for Tb, Dy, Ho and A-type antiferromagnetic for Er.","lead":"Neutron diffraction experiments on four rare-earth kagome metals (Tb, Dy, Ho, Er)V6Sn6 reveal their low-temperature magnetic structures: Tb and Ho order ferromagnetically with moments along the c axis, Dy with moments tilted 20 degrees from c, and Er with alternating magnetic layers. The results give experimentalists a firm basis for testing how magnetism couples to the topological electron bands in this widely studied material family.","discovery_kind":"extension","skeptic_critique":{"model":"deepseek-v4-flash","headline":"DyV6Sn6's ~20° tilt and the Dy/Er moment magnitudes rest on a large, crystal-shape-dependent neutron absorption correction (Dy: ~994 b); without an independent cross-check, the headline quantitative claims are not fully secure.","rationale":"The reader's weakest assumption—the accuracy of the neutron absorption correction for Dy and Er—is also the most load-bearing concern I find. The qualitative magnetic structures (FM for Tb/Dy/Ho, A-type AFM for Er) are well supported by magnetization anisotropy, heat capacity anomalies, and the clear presence of half-integer magnetic peaks for Er. However, the specific quantitative claims for Dy—the 20° tilt and the 6.6(2) µB moment—depend on corrected intensities from a crystal with a very large absorption cross-section, and no cross-validation is reported. The tilt angle is a headline result and is not independently required by the bulk measurements, making it the most fragile element of the central claim. I also note an internal inconsistency: Table II shows the TbV6Sn6 V(6i) coordinate shifting from 0.2562(4) at 5.5 K to 0.2488(4) at 1.6 K, yet the text says no appreciable atomic-position changes occur; this is secondary because V is a weak neutron scatterer and the Tb structure is corroborated by bulk measurements. Given the absence of deposited intensity data and the model dependence of the absorption correction, I would adjust the verdict from ACCEPT to CONDITIONAL: the paper should be accepted only if the authors validate the absorption correction (e.g., by an alternative absorption model or a shorter-wavelength measurement) or make the corrected and uncorrected reflection lists available for re-refinement.","tokens_in":22194,"tokens_out":11483,"duration_ms":114398,"concrete_test":"Re-refine the DyV6Sn6 intensities with an independent absorption treatment, e.g., a numerical absorption correction in JANA2006 or FullProf using the same indexed crystal faces, or remeasure the same crystal at a shorter wavelength (about 0.7 Å) where the Dy absorption cross-section is reduced by roughly 2-3x. If the refined tilt angle changes by more than 5° or the ab component shifts by more than 1 µB, the claimed 20° tilt is an absorption artifact. If the tilt and moment agree within uncertainties, the concern is resolved.","verdict_should_be":"CONDITIONAL","load_bearing_attack":"The central quantitative claim for DyV6Sn6—a ~20° tilt off the c axis with ordered moment 6.6(2) µB—is extracted from single-crystal neutron intensities after a Mag2Pol absorption correction. Dy has a thermal-neutron absorption cross-section of about 994 b, so the correction is large and strongly path-length dependent. The tilt is determined from the ratio of the ab-plane component (M[1,0,0]=2.3(2) µB) to the c-axis component (M[0,0,1]=6.2(1) µB). For a plate-shaped crystal mounted in the (H,H,L) plane, reflections that probe the ab component and those that probe the c component sample very different neutron path lengths through the sample. A small error in the Mag2Pol crystal-shape model—or in the assumed sample shape, orientation, or composition—can systematically bias this ratio and thus directly shift the refined tilt angle and the moment magnitudes. The magnetization data for Dy show only weak anisotropy and do not require a tilt, so the 20° tilt rests entirely on the diffraction refinement. ErV6Sn6 (absorption ~159 b) is similarly affected for its moment magnitude, though its A-type AFM propagation vector is robust. The manuscript does not report raw or absorption-corrected reflection lists, so the correction cannot be independently audited from the preprint.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"This paper reports the ground-state magnetic structures of four recently discovered V-based kagome metals, RV6Sn6 (R = Tb, Dy, Ho, Er), determined by single-crystal neutron diffraction and supported by magnetization and heat-capacity measurements. The authors find collinear ferromagnetic order for TbV6Sn6 and HoV6Sn6 with moments along c, ferromagnetic order for DyV6Sn6 with moments tilted approximately 20 degrees from c, and A-type antiferromagnetic order for ErV6Sn6 with propagation vector k = (0,0,0.5) and moments in the ab plane. Ordered moments are reported as 9.4(2), 6.6(2), 6.4(2), and 6.1(2) uB for Tb, Dy, Ho, and Er, respectively. The paper also compares these structures with those of the RMn6Sn6 series and discusses implications for magnetism-topology interplay.","tokens_in":22460,"tokens_out":6696,"duration_ms":69707,"significance":"If the quantitative results hold, this paper fills an important gap: the ground-state magnetic structures of the magnetic RV6Sn6 kagome metals were previously undetermined, and these structures are directly relevant to proposed topological phases in this family. The study is experimental and does not sell a derivation as a prediction; the fitted moments are observables obtained from symmetry-constrained refinements against measured intensities. Strengths include the use of multiple neutron facilities, substantial reflection sets (135-245 reflections per compound), good refinement residuals (RF factors between 1.96 and 5.53), and corroborating checks: the unchanged (0,0,2) and (0,0,6) structural reflections support the c-axis easy-axis assignments for Tb and Ho, and the Er propagation vector is supported by magnetic peaks at L+0.5 with a check against second-order contamination. The broad structural classifications (FM vs AFM, easy-axis orientations) are robust.","major_comments":[{"comment":"The central quantitative claims—the approximately 20-degree tilt in DyV6Sn6 and the ordered moments of DyV6Sn6 and ErV6Sn6—are obtained from reflection intensities after a Mag2Pol absorption correction. Because the thermal-neutron absorption cross-sections of Dy and Er are about 994 b and 159 b, respectively, and the crystals are plate-shaped, the corrected intensity ratio between ab-plane-sensitive and c-axis-sensitive reflections depends strongly on the shape model, sample orientation, composition, and path-length distribution. The manuscript does not provide raw or absorption-corrected reflection lists, the Mag2Pol crystal-shape parameters, or a sensitivity analysis. The Dy tilt angle is essentially set by |M[1,0,0]|/|M[0,0,1]| = 2.3(2)/6.2(1), so a systematic error in this ratio directly shifts the headline tilt angle and the moment magnitude. I request that the authors include the reflection tables, the Mag2Pol model parameters (faceted shape, dimensions, orientation), and a demonstration that the tilt and moments are stable under reasonable variations of the model or are otherwise independently corroborated.","section":"§IV (absorption correction paragraph) and Table II"},{"comment":"The Er structure is refined with the Γ9 basis vectors ψ2 = (1,0,0) and ψ3 = (1,2,0), giving M[1,0,0] = 6.1(3) µB and M[1,2,0] = 0, i.e., a single a-axis magnetic domain. In a hexagonal crystal with k = (0,0,0.5), three in-plane domain orientations are generally allowed. For DyV6Sn6 the authors explicitly state that an equally-populated-domain refinement was also performed, but for ErV6Sn6 no equivalent domain-population treatment is described. If the crystal contains multiple magnetic domains, refining with a single-domain model can bias the refined moment magnitude and direction. Please state the domain assumption for Er, refine or justify the domain populations, or provide evidence that the crystal is genuinely single-domain.","section":"§IV.D (ErV6Sn6) and Table II"}],"minor_comments":[{"comment":"The Er ordered moment is quoted as 6.1(2) µB in the abstract and conclusions, whereas Table II and §IV.D give 6.1(3) µB; please reconcile these values.","section":"Abstract and §VI"},{"comment":"The phrase 'The ordered magnetic moment are determined' appears in the abstract and conclusions; it should be 'The ordered magnetic moments are determined'.","section":"§IV and §VI"},{"comment":"The caption says 'custom and top view'; this is presumably a typo for 'cutaway and top view' or similar, and should be clarified.","section":"Fig. 9 caption"},{"comment":"The T_bV6Sn6 transition temperature is reported as 4.3 K from neutron diffraction, 4.0 K from magnetization, and ~3.6 K from the heat-capacity anomaly. The text calls these consistent without explaining the criteria (e.g., onset vs peak vs midpoint); please specify the definition used for each value.","section":"Table I, Table II, and Fig. 5"},{"comment":"The caption describes RF(Int) only qualitatively as an average discrepancy between observed and calculated integrated intensities; please give the exact formula so the goodness of fit is reproducible.","section":"Table II caption"},{"comment":"In the sentence about absorption cross-sections, 'other rare-rare elements' should read 'other rare-earth elements'.","section":"§II"}],"recommendation":"major_revision","confidential_remarks":"The experimental classifications are likely sound, and the paper would be a good addition to the field. My reservation concerns the audibility of the quantitative Dy and Er moments: the absorption correction is large and shape-dependent, and the manuscript does not include the reflection tables or correction parameters needed to verify it. I would be comfortable with acceptance after the authors supply the requested absorption documentation, reflection lists, and Er domain-population clarification."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"First, the headline: this is the first single-crystal neutron diffraction determination of the ground-state magnetic structures for TbV6Sn6, DyV6Sn6, HoV6Sn6, and ErV6Sn6. That alone makes it a reference paper for the RV6Sn6 kagome family. The qualitative picture—Tb and Ho collinear FM along c, Dy FM tilted ~20° from c, Er A-type AFM with k=(0,0,0.5) and moments in the ab plane—is well supported by the diffraction data and consistent with the magnetization and heat capacity they report. The refinements use a reasonable number of reflections (135–245) and the residuals are good (RF 1.96–5.53). I also appreciate the explicit comparison to the RMn6Sn6 series; it's a useful framing.\n\nThe main soft spot is the absorption correction for Dy and Er. Dy has a thermal-neutron absorption cross-section of ~994 b, Er ~159 b. The refined tilt angle and moment magnitudes for Dy, and the moment magnitude for Er, depend on a Mag2Pol correction that uses a model of the crystal shape. The manuscript does not include raw or absorption-corrected reflection tables, so a referee can't independently check how sensitive the results are to the assumed shape. This is a real quantitative concern, but it doesn't threaten the qualitative classification: the FM vs AFM assignments come from the presence/absence of magnetic reflections, and the easy-axis directions are corroborated by the zero change in (0,0,2)/(0,0,6) for Tb and Ho and the L+0.5 positions for Er. So I would treat the 20° tilt for Dy and the specific moment values as provisional until a cross-check appears, but the paper's central claims are most likely right.\n\nA minor note: the TbV6Sn6 lattice expansion at 1.6 K is flagged as unusual. It's good that they report it and call for follow-up; it doesn't undermine the magnetic structure.\n\nWho is this for? Anyone working on kagome magnets, especially the RV6Sn6 and RMn6Sn6 families, and people interested in rare-earth magnetism in topological metals. It deserves serious peer review. My recommendation: accept after the authors make the reflection tables available as supplementary material, and ideally add a sensitivity analysis of the absorption correction for Dy. If they can't provide raw data, at least a statement of the crystal shape parameters used.","headline":"First single-crystal neutron determination of the RV6Sn6 ground-state magnetic structures; a solid reference paper, but the Dy tilt and Dy/Er moment magnitudes should be treated as provisional until the absorption correction is auditable.","tokens_in":23085,"tokens_out":2536,"would_cite":true,"duration_ms":25073,"reading_group":"yes","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"Neutron diffraction determines that TbV6Sn6, DyV6Sn6, and HoV6Sn6 order ferromagnetically while ErV6Sn6 orders as an A-type antiferromagnet, with moments of 9.4, 6.6, 6.4, and 6.1 Bohr magnetons respectively.","keywords":["kagome metal","RV6Sn6","neutron diffraction","magnetic structure","rare-earth magnetism","ferromagnet","A-type antiferromagnet","single-ion anisotropy"],"falsifier":"Re-measure DyV6Sn6 on a diffractometer with a much shorter neutron wavelength (where absorption is small) or with an independently determined crystal shape, then refine the tilt angle; if the refined tilt differs from 20 degrees by more than the reported uncertainty, the tilted ferromagnetic claim would need revision. For ErV6Sn6, a powder neutron-diffraction pattern at 50 mK must show magnetic peaks only at half-integer L positions with the moment in the ab plane; the appearance of any other propagation vector or a c-axis moment component would falsify the A-type antiferromagnetic assignment.","tokens_in":21984,"feed_emoji":"🧲","tokens_out":5674,"duration_ms":54172,"temperature":0.7,"pith_summary":"The paper aims to determine the zero-field ground-state magnetic structures of four recently discovered kagome metals, RV6Sn6 with R = Tb, Dy, Ho, Er, using single-crystal neutron diffraction. It establishes that TbV6Sn6 and HoV6Sn6 order as collinear ferromagnets with moments along the hexagonal c axis, DyV6Sn6 as a ferromagnet with moments tilted about 20 degrees from c, and ErV6Sn6 as an A-type antiferromagnet with the c axis doubled and moments lying in the ab plane. Knowing these structures matters because these materials host topological kagome bands, and the magnetic order is the key tuning parameter for the interplay between magnetism and band topology. The paper also reports crystal growth, magnetization, and heat-capacity data that corroborate the ordering and place the transition temperatures at 4.3, 3.0, 2.4, and 0.6 K for Tb, Dy, Ho, and Er, respectively.","feed_headline":"Tb, Dy, Ho kagome metals are ferromagnets; Er is antiferromagnet","feed_subtitle":"Neutron diffraction pins down the ordered moments and spin directions researchers need to probe topology-magnetism interplay.","key_machinery":"The central machinery is single-crystal neutron diffraction combined with magnetic crystallography: measuring nuclear and magnetic Bragg intensities above and below the transition, identifying the magnetic propagation vector from the positions of magnetic reflections, and refining the ordered-moment components against basis vectors obtained from representational analysis of space group P6/mmm. For the ferromagnetic compounds the propagation vector is $\\mathbf{k} = (0,0,0)$; for ErV6Sn6 it is $\\mathbf{k} = (0,0,0.5)$, which doubles the magnetic cell along c. The refinements use basis vectors such as $\\psi_1 = (0,0,1)$ for c-axis moments and $\\psi_2 = (1,0,0)$, $\\psi_3 = (1,2,0)$ for in-plane moments. The argument also relies on a crystal-shape-based absorption correction for Dy and Er, whose thermal-neutron absorption cross-sections are 994 and 159 barn respectively.","core_discovery":"The authors find that the ground states of the four kagome metals split into two magnetic families. TbV6Sn6 and HoV6Sn6 are collinear ferromagnets with ordered moments of 9.4(2) and 6.4(2) Bohr magnetons aligned along the c axis. DyV6Sn6 is also a ferromagnet, but its 6.6(2) Bohr magneton moment is tilted approximately 20 degrees away from the c axis toward the [1,0,0] direction. ErV6Sn6 is an A-type antiferromagnet with propagation vector $\\mathbf{k} = (0,0,0.5)$, meaning ferromagnetic ab-plane layers stack antiferromagnetically along c, and its 6.1(2) Bohr magneton moments lie in the ab plane. These assignments come from refining up to 245 measured neutron reflections against symmetry-allowed basis vectors derived for space group P6/mmm, with neutron absorption corrections applied to the strongly absorbing Dy and Er compounds.","pith_inferences":["If the 20-degree Dy tilt survives a future measurement with an independent absorption correction, it implies a fine balance between in-plane and out-of-plane single-ion anisotropy; one testable consequence is a field-induced spin reorientation at modest fields, visible as an anomaly in magnetostriction or magnetization derivative.","The A-type antiferromagnet ErV6Sn6, with moments confined to the ab plane, may develop a weak net in-plane moment if magnetic domains are imbalanced; measuring magnetization on a detwinned or field-cooled crystal could reveal this.","Comparing angle-resolved photoemission above and below the ordering temperatures in these compounds could isolate how the rare-earth order alters the kagome Dirac bands, a measurement not reported in this paper but enabled by its structural assignments.","The heat-capacity data show broad low-temperature features attributed to nuclear Schottky contributions; a dedicated analysis of those contributions, combined with the moment sizes reported here, could put constraints on the hyperfine coupling constants of the rare-earth ions."],"forward_implications":["TbV6Sn6 and HoV6Sn6 have a collinear ferromagnetic ground state with out-of-plane moments, the same symmetry setting used in TbMn6Sn6 to realize a quantum-limit Chern gap, so these compounds become direct candidates for testing similar topological responses with an ordered out-of-plane moment.","DyV6Sn6's tilted ferromagnetic state provides a clean case of competing single-ion anisotropy: the tilt angle is a measurable quantity that any microscopic model of the crystal-field anisotropy must reproduce.","ErV6Sn6's A-type antiferromagnetic order with an in-plane moment and doubled c axis means its zero-field ground state carries no net magnetization, yet it can be field-tuned toward a polarized state, which is a natural platform for field-dependent transport and Hall measurements.","The ordered moments of 9.4, 6.6, 6.4, and 6.1 Bohr magnetons are all below the corresponding free-ion effective moments, indicating that crystalline-electric-field effects quench the moments; inelastic neutron scattering to map the crystal-field levels would follow directly from this result.","Because the V kagome layers are nonmagnetic in this series, the magnetic order couples to the topological bands only through the rare-earth layers, making RV6Sn6 a controlled system for separating magnetism from the kagome electronic structure."],"supporting_citations":[{"why":"Supplies the earlier single-crystal magnetization and heat-capacity characterization of RV6Sn6 that this work extends with neutron diffraction, including transition temperatures and anisotropic susceptibility baselines.","marker":"[58]"},{"why":"Reports the electronic and magnetic properties of RV6Sn6 (R = Tb-Tm) and notes the absence of magnetic order in ErV6Sn6 above 1.8 K, motivating the dilution-refrigerator measurements used here.","marker":"[59]"},{"why":"Establishes uniaxial ferromagnetism with an easy c axis in TbV6Sn6, supporting the c-axis-aligned ferromagnetic model refined in this work.","marker":"[63]"},{"why":"Documents highly anisotropic, Ising-like magnetism in TbV6Sn6, which backs the choice of a single out-of-plane basis vector in the Tb refinement.","marker":"[64]"},{"why":"Provides magnetic and magnetotransport evidence for ferromagnetic interaction along c and antiferromagnetic interaction within the ab plane in DyV6Sn6 and HoV6Sn6, informing the refinement models for those two compounds.","marker":"[67]"},{"why":"Supplies the absorption-correction and magnetic-structure refinement program used to correct the Dy and Er datasets and to refine the reported moment components.","marker":"[69]"},{"why":"Provides the representational-analysis protocol used to compute the allowed basis vectors for the magnetic structures in space group P6/mmm.","marker":"[74]"},{"why":"Gives the RMn6Sn6 (R = Gd-Er) magnetic structures that form the comparison basis for discussing how removing Mn magnetism changes the rare-earth ordering.","marker":"[45]"}],"fun_headline_variants":["Kagome metals: Tb, Dy, Ho ferromagnetic; Er antiferromagnetic","Neutron study reveals three FM, one AFM in kagome metals","Magnetic order in RV6Sn6: Tb, Dy, Ho FM; Er AFM","Ferromagnetic Tb, Dy, Ho vs antiferromagnetic Er in kagome metals","Kagome metal ground states: three ferromagnets, one antiferromagnet"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The neutron-absorption correction for the strongly absorbing dysprosium and erbium crystals is accurate enough that the corrected reflection intensities, and therefore the refined moment sizes and the 20-degree Dy tilt, are not systematically biased.","fun_headline_variants_meta":{"raw":{"variants":["Kagome metals: Tb, Dy, Ho ferromagnetic; Er antiferromagnetic","Neutron study reveals three FM, one AFM in kagome metals","Magnetic order in RV6Sn6: Tb, Dy, Ho FM; Er AFM","Ferromagnetic Tb, Dy, Ho vs antiferromagnetic Er in kagome metals","Kagome metal ground states: three ferromagnets, one antiferromagnet"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000654,"raw_usage":{"total_tokens":3096,"prompt_tokens":1143,"completion_tokens":1953,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":759,"completion_tokens_details":{"reasoning_tokens":1839}},"tokens_in":759,"tokens_out":1953,"duration_ms":14032,"temperature":1.0,"reasoning_tokens":1839,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-12T15:12:15.943502+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Re-measure DyV6Sn6 on a diffractometer with a much shorter neutron wavelength (where absorption is small) or with an independently determined crystal shape, then refine the tilt angle; if the refined tilt differs from 20 degrees by more than the reported uncertainty, the tilted ferromagnetic claim would need revision. For ErV6Sn6, a powder neutron-diffraction pattern at 50 mK must show magnetic peaks only at half-integer L positions with the moment in the ab plane; the appearance of any other propagation vector or a c-axis moment component would falsify the A-type antiferromagnetic assignment.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the earlier single-crystal magnetization and heat-capacity characterization of RV6Sn6 that this work extends with neutron diffraction, including transition temperatures and anisotropic susceptibility baselines."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Establishes uniaxial ferromagnetism with an easy c axis in TbV6Sn6, supporting the c-axis-aligned ferromagnetic model refined in this work."},{"cited_title":"Porter, G","cited_arxiv_id":null,"evidence_quote":"Documents highly anisotropic, Ising-like magnetism in TbV6Sn6, which backs the choice of a single out-of-plane basis vector in the Tb refinement."},{"cited_title":"Huang, Z","cited_arxiv_id":null,"evidence_quote":"Provides magnetic and magnetotransport evidence for ferromagnetic interaction along c and antiferromagnetic interaction within the ab plane in DyV6Sn6 and HoV6Sn6, informing the refinement models for those two compounds."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Supplies the absorption-correction and magnetic-structure refinement program used to correct the Dy and Er datasets and to refine the reported moment components."},{"cited_title":"Mirebeau, A","cited_arxiv_id":null,"evidence_quote":"Provides the representational-analysis protocol used to compute the allowed basis vectors for the magnetic structures in space group P6/mmm."},{"cited_title":"Venturini, R","cited_arxiv_id":null,"evidence_quote":"Gives the RMn6Sn6 (R = Gd-Er) magnetic structures that form the comparison basis for discussing how removing Mn magnetism changes the rare-earth ordering."}],"review_version":1}