{"id":"13bbd6fb-9312-4d73-ad31-49c6707e59b5","arxiv_id":"1908.07003","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":5,"one_line_summary":"This paper predicts via atomistic simulations that amorphous Gd25Co75 films can host stable sub-10 nm Neel skyrmions at room temperature when the interfacial DMI is around 1.0 to 1.2 mJ/m2.","lead":"This paper uses computer simulations to show that ultra-small magnetic whirlpools called skyrmions can remain stable at room temperature in thin films of an amorphous ferrimagnet. If correct, the result points toward denser, faster, and lower-power magnetic memory and logic devices.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"Sub-10 nm claim rests on an unspecified DMI decay length and unreported exchange parameters; the 10 nm phase diagram should be re-run with explicit decay lengths and the correct Co/Pt DMI reference.","rationale":"The reader identified the unspecified DMI profile and missing material parameters as the weakest assumption, and I agree: the sub-10 nm stability window is a quantitative prediction whose key inputs are not reported. The exponential-decay DMI profile is especially load-bearing because the paper compares interfacial DMI values to experiment, but the effective DMI inside a 10 nm film depends on the decay length, which is never given. The citation error for reference [17] further weakens the experimental anchoring. These issues do not prove the result wrong, but they make independent verification impossible. The reader's CONDITIONAL verdict is appropriate, and I do not see grounds to strengthen or weaken it. I would keep the recommendation as CONDITIONAL, with the condition that the DMI decay length, exchange constants, and atomic moments be reported and the phase diagram re-run with varied decay lengths.","tokens_in":5513,"tokens_out":3830,"duration_ms":41679,"concrete_test":"Re-run the thickness-DMI phase diagram in Figure 5 for the 10 nm film with three explicit DMI decay lengths (for example 0.5, 1.0, and 2.0 nm) while holding K = 3 x 10^4 J/m3 and all other Hamiltonian parameters fixed at their reported values, and check whether sub-10 nm skyrmions remain stable for interfacial DMI between 1.0 and 1.2 mJ/m2. If the stability window persists across decay lengths, the concern is resolved; if it shifts or disappears, the central claim is not robust.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim, stated in the Conclusions, is that sub-10 nm skyrmions form in 10 nm Gd25Co75 films for interfacial DMI near 1.0–1.2 mJ/m2. This prediction depends directly on the exponential-decay DMI profile introduced in the Results and on the atomistic Hamiltonian in Eq. (1). The paper never states the DMI decay length, the exchange constants J_CoCo, J_GdGd, and J_GdCo, or the atomic moments used for Gd25Co75. For a 10 nm film, an interfacial DMI of 1.0 mJ/m2 with a short decay length (about 1 nm) deposits much less total DMI through the thickness than the same interfacial value with a longer decay length (about 3 nm), which will shift both the skyrmion size and the stability window. The comparison to experiment is also weakened by the citation: reference [17] (Stashkevich et al.) measures Py/Pt, not Co/Pt, so the statement that the 1.0–1.2 mJ/m2 range matches measured Co/Pt interfacial DMI lacks support in the text. Without fixed, reported parameters, the quantitative sub-10 nm result cannot be independently reproduced, and the central claim is not yet robust.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper reports atomistic Landau-Lifshitz-Gilbert simulations of room-temperature Néel skyrmions in amorphous Gd25Co75 ferrimagnetic films with interfacial Dzyaloshinskii-Moriya interaction (DMI). Using an exponential-decay profile for the interfacial DMI, the authors map phase diagrams in anisotropy–DMI space for 5-nm films and in DMI–thickness space for 5–10 nm films at 300 K. They report a 13 nm skyrmion at K = 3 × 10^4 J/m3 with interfacial DMI ~0.6 mJ/m2, a ~20 nm skyrmion at interfacial DMI ~0.9 mJ/m2 consistent with Caretta et al.'s experiment, and sub-10 nm skyrmions in 10-nm films for interfacial DMI in the range 1.0–1.2 mJ/m2. A tomographic view is used to claim that the skyrmion spin texture is columnar through the film thickness. The central conclusion is that amorphous ferrimagnets can host ultra-small, room-temperature, columnar Néel skyrmions at experimentally plausible DMI strengths.","tokens_in":5785,"tokens_out":3549,"duration_ms":35611,"significance":"If the quantitative prediction is robust, the paper identifies a concrete material platform for sub-10 nm room-temperature skyrmions, which is directly relevant to skyrmion-based memory and logic devices. The use of an amorphous structure from ab initio molecular dynamics and an external experimental benchmark (Caretta et al.) are strengths: the simulation is not fitted to the target skyrmion size. However, the central quantitative claim is currently supported by unreported model parameters and by a mis-cited experimental reference, so the significance cannot yet be assessed independently. A revised version that supplies the Hamiltonian parameters, the DMI decay length, and a correct experimental comparison would make the prediction reproducible and materially strengthen the paper.","major_comments":[{"comment":"The values of the exchange constants J_CoCo, J_GdGd, and J_GdCo, the atomic moments μi used for Gd and Co, and the exponential decay length of the interfacial DMI are never specified. Since the effective DMI torque through a 10-nm film depends exponentially on the decay length, the sub-10 nm skyrmion window in Figure 5 and the quantitative comparison near 0.9 mJ/m2 in Figure 4 are not reproducible with the information given. Please report all atomistic Hamiltonian parameters and a sensitivity study over the DMI decay length (e.g., 1–3 nm) to show that the sub-10 nm result is not an artifact of the chosen profile.","section":"Results and Discussion, Eq. (1)"},{"comment":"The text states that the 1.0–1.2 mJ/m2 range is 'in the range of measured interfacial DMI in Co/Pt films [17]', but reference [17] (Stashkevich et al.) reports measurements on Py/Pt, not Co/Pt. This citation error removes the stated experimental support for the DMI range used for the 10-nm sub-10 nm skyrmions. Please cite a Co/Pt or GdCo/Pt interfacial DMI measurement, or clearly rephrase the claim if the comparison is only to Py/Pt.","section":"Results and Discussion, Figure 5 and reference [17]"},{"comment":"The conversion from Caretta et al.'s average DMI of 0.12 mJ/m2 to an interfacial DMI of about 0.9 mJ/m2 is asserted without derivation. The meaning of 'average DMI' and the thickness or profile used for the conversion should be given explicitly, because the claimed agreement between simulation and experiment depends on this conversion. If the conversion is simply multiplication by film thickness or by an assumed decay integral, that assumption should be stated and justified.","section":"Results and Discussion, Caretta et al. comparison"}],"minor_comments":[{"comment":"'Tomograph' should be 'Tomography'.","section":"Figure 6 caption"},{"comment":"The phrase 'DMI values similar to that obtained in experiment' is ambiguous: the preceding comparison is to Caretta et al.'s average DMI of 0.12 mJ/m2, converted to about 0.9 mJ/m2, whereas the 10-nm film uses 1.0–1.2 mJ/m2. Please restate which experimental quantity is being compared and how the conversion is made.","section":"Conclusions"},{"comment":"For the phase diagrams in Figures 4 and 5, the criteria used to classify a state as 'skyrmion' versus 'stripe' or 'ferrimagnetic', and the definition of skyrmion diameter, are not stated. A sentence defining the diameter measure and the stability criterion (e.g., persistence over a simulation time) would remove ambiguity for the sub-10 nm claim.","section":"Results and Discussion"},{"comment":"There are minor grammatical and typographical issues, including 'skyrmion ha s emerged' in the abstract and 'e.g. ~10 nm or smaller in diameter, skyrmions can be easier to unpin' in the Introduction. A careful proofread is needed.","section":"Abstract and Introduction"}],"recommendation":"major_revision","confidential_remarks":"The manuscript appears to be a short proceedings-style contribution. The central scientific idea is promising, but the missing Hamiltonian parameters and the incorrect experimental citation are load-bearing for the central claim. I would be willing to review a revised version that reports the full parameter set and a correct experimental comparison. If the authors cannot provide the DMI decay length or exchange parameters, the quantitative sub-10 nm claim should be withdrawn or substantially softened."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague,\n\nThis paper is a plausible simulation study of room-temperature skyrmions in amorphous Gd25Co75, with a specific and externally checkable prediction: sub-10 nm skyrmions in 10 nm films at interfacial DMI around 1.0–1.2 mJ/m2. The workflow is standard atomistic LLG with a stochastic field, and the comparison to Caretta's measured 10–30 nm skyrmions gives one honest consistency point. The phase diagrams in Figs 4 and 5 appear internally consistent: larger DMI enlarges skyrmions, higher anisotropy shrinks them, and thicker films require stronger interfacial DMI. Those trends are physically sensible.\n\nThe soft spots are real but not fatal. The paper never states the DMI decay length, the exchange constants Jij, or the atomic moments, even though these are the inputs that determine whether sub-10 nm skyrmions actually form in a 10 nm film. The exponential-decay DMI profile is referenced to calculations and experiments, but the decay length is never specified, and the citation used to justify the 1.0–1.2 mJ/m2 range is ref. 17, which is actually Py/Pt, not Co/Pt. That misattribution matters because the claimed match between simulation and measured Co/Pt DMI is unsupported. No code or data are shipped, so independent verification would require emailing the authors. None of these flaws proves the result wrong, but they do mean the quantitative sub-10 nm claim is not independently reproducible from the manuscript.\n\nOne minor thing: the paper is written as a tribute to Geballe, so the introduction spends a paragraph on that. Not a problem, but the prose is uneven.\n\nOverall, the central physical idea — amorphous ferrimagnets as a host for ultra-small room-temperature skyrmions — is worth taking seriously, and the paper makes a concrete thickness-DMI prediction that experiments could test. But the lack of parameter reporting and the reference error would need to be fixed before I would rely on the specific numbers. I would send it to a referee; a good referee would ask for the parameters and a corrected citation.","headline":"A plausible simulation prediction of sub-10 nm skyrmions in amorphous GdCo, but missing key parameters and a misattributed DMI reference keep it from being reproducible as written.","tokens_in":6365,"tokens_out":1927,"would_cite":false,"duration_ms":19176,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":["75.70.Kw","75.50.Gg"],"model":"deepseek-v4-flash","headline":"Atomistic simulations predict room-temperature Néel skyrmions smaller than 10 nm in amorphous Gd25Co75 films, stable at experimentally accessible interfacial DMI values.","keywords":["amorphous ferrimagnet","Néel skyrmion","Dzyaloshinskii-Moriya interaction","atomistic simulation","Gd25Co75","room-temperature skyrmion","perpendicular magnetic anisotropy","spintronics"],"falsifier":"Image a 10-nm amorphous Gd25Co75 film on Pt or Ir at 300 K with $K\\approx 3\\times10^4$ J/m$^3$ and measure the interfacial DMI: if the surface DMI is below about 1 mJ/m2, or no stable sub-10 nm skyrmions are found in the 1.0–1.2 mJ/m2 window, the central prediction fails. A depth-resolved magnetic imaging experiment that shows the skyrmion texture is not columnar through the film would also falsify the claim.","tokens_in":5281,"feed_emoji":"🌀","tokens_out":6157,"duration_ms":58961,"temperature":0.7,"pith_summary":"This paper argues that amorphous rare-earth–transition-metal ferrimagnets, specifically Gd25Co75, can stabilize room-temperature Néel skyrmions far smaller than those typically found in crystalline ferromagnet heterostructures. Using atomistic simulations, it finds stable sub-10 nm skyrmions in 10-nm-thick films when the interfacial Dzyaloshinskii–Moriya interaction lies between 1.0 and 1.2 mJ/m2, a range already measured in Co/Pt systems. The paper also reports that the skyrmion spin texture runs columnarly through the film thickness despite the exponential decay of the interfacial DMI. This matters because skyrmion-based memory and logic require stable, tiny, mobile magnetic bits, and the predicted sizes are in the regime needed for high-density spintronic devices.","feed_headline":"Sub-10 nm skyrmions predicted in amorphous ferrimagnets","feed_subtitle":"Room-temperature GdCo films can hold ultra-small Néel skyrmions at DMI strengths already seen in experiments.","key_machinery":"The argument is carried by an atomistic spin Hamiltonian with nearest-neighbor exchange, Dzyaloshinskii–Moriya interaction, perpendicular anisotropy, external field, and demagnetization terms, evolved by stochastic Landau–Lifshitz–Gilbert dynamics. The decisive modeling choice is an exponential depth decay of the interfacial DMI away from the heavy-metal interface, so the DMI acts strongly only near the interface; the model nonetheless produces columnar skyrmions spanning the entire 10-nm film. The amorphous Gd25Co75 structure supplies two coupled sublattices and low net magnetization, which the paper identifies as the reason such small skyrmions can be stable at room temperature with only moderate anisotropy.","core_discovery":"The paper's central claim is a predicted stability window: at 300 K, amorphous Gd25Co75 films of 10 nm thickness host Néel skyrmions with diameters below 10 nm for interfacial DMI values around 1.0–1.2 mJ/m2 and perpendicular anisotropy $K\\approx 3\\times10^4$ J/m$^3$. In 5-nm films the same model gives 13-nm skyrmions at $D\\approx0.6$ mJ/m2 and about 20-nm skyrmions at $D\\approx0.9$ mJ/m2, which matches reported skyrmion sizes in Pt/GdCo/TaOx. The paper further claims that the ferrimagnet's two antiferromagnetically coupled sublattices and small net magnetization, combined with interfacial DMI, make these ultra-small skyrmions robust and columnar through the full film thickness rather than confined to the interface.","pith_inferences":["Because the paper does not fix the DMI decay length for GdCo, a testable extension is to vary that decay length in the simulation; the sub-10 nm window in 10-nm films should shift or close if the true decay is significantly shorter than assumed.","The same atomistic model could be applied to other rare-earth–transition-metal ferrimagnets, such as GdFeCo or TbCo, to map which compositions and thicknesses give the smallest stable skyrmions at 300 K.","The result implies a design rule opposite to the usual one: rather than maximizing perpendicular anisotropy, ultra-small skyrmions in amorphous ferrimagnets may only need moderate anisotropy around $10^4$ J/m$^3$ combined with a tuned interfacial DMI."],"forward_implications":["Room-temperature skyrmions below 10 nm should be achievable in amorphous ferrimagnet films using interfacial DMI values already observed in heavy-metal/ferromagnet stacks, without requiring exotic materials.","The predicted 20-nm skyrmion at $D\\approx0.9$ mJ/m2 in 5-nm GdCo matches measured sizes in Pt/GdCo/TaOx, so the simulated phase diagram can be used to target specific skyrmion sizes by choosing film thickness and DMI.","Columnar skyrmions in 10-nm films imply that thicker magnetic layers can serve as device elements, giving larger signal and less stringent fabrication constraints than ultrathin ferromagnet alternatives.","Near the magnetization-compensation point, the ferrimagnet's small net moment supports fast current-driven motion and a reduced skyrmion Hall effect, making these ultra-small skyrmions suited for racetrack-type memory and logic architectures."],"supporting_citations":[{"why":"provides the amorphous Gd25Co75 atomic structure from ab initio molecular dynamics, the substrate for all simulations.","marker":"[15]"},{"why":"supports the exponential-decay law used to model interfacial DMI inside the magnetic layer.","marker":"[16]"},{"why":"supplies the measured interfacial DMI range around 1.0–1.2 mJ/m2 that the sub-10 nm stability window is compared against.","marker":"[17]"},{"why":"supplies the perpendicular anisotropy value K≈3×10^4 J/m3 used in the phase diagrams.","marker":"[18]"},{"why":"reports experimental 10–30 nm skyrmions in Pt/GdCo/TaOx, the benchmark for the simulated size-versus-DMI relation.","marker":"[13]"},{"why":"provides evidence of reduced skyrmion Hall effect in ferrimagnetic films, supporting the device-motivation part of the claim.","marker":"[14]"}],"fun_headline_variants":["Sub-10 nm skyrmions predicted at room temperature","Amorphous ferrimagnets enable ultra-small skyrmions at 300 K","Room-temperature skyrmions under 10 nm in GdCo films","Tiny skyrmions predicted in amorphous GdCo at 300 K"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing assumption is that interfacial DMI in GdCo decays exponentially into the film with a length scale and magnitude close to the values used in the simulation; if the real DMI is much weaker, shorter-ranged, or different in profile, the predicted sub-10 nm skyrmions will not form.","fun_headline_variants_meta":{"raw":{"variants":["Sub-10 nm skyrmions predicted at room temperature","Amorphous ferrimagnets enable ultra-small skyrmions at 300 K","Room-temperature skyrmions under 10 nm in GdCo films","Tiny skyrmions predicted in amorphous GdCo at 300 K"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000319,"raw_usage":{"total_tokens":1742,"prompt_tokens":829,"completion_tokens":913,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":445,"completion_tokens_details":{"reasoning_tokens":836}},"tokens_in":445,"tokens_out":913,"duration_ms":8086,"temperature":1.0,"reasoning_tokens":836,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-14T12:29:09.666584+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Image a 10-nm amorphous Gd25Co75 film on Pt or Ir at 300 K with $K\\approx 3\\times10^4$ J/m$^3$ and measure the interfacial DMI: if the surface DMI is below about 1 mJ/m2, or no stable sub-10 nm skyrmions are found in the 1.0–1.2 mJ/m2 window, the central prediction fails. A depth-resolved magnetic imaging experiment that shows the skyrmion texture is not columnar through the film would also falsify the claim.","supporting_citations":[{"cited_title":"Nature 439, 419-425 (2006)","cited_arxiv_id":null,"evidence_quote":"provides the amorphous Gd25Co75 atomic structure from ab initio molecular dynamics, the substrate for all simulations."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"supports the exponential-decay law used to model interfacial DMI inside the magnetic layer."},{"cited_title":"A, Belmeguenai, M., Roussigné, Y., Cherif, S","cited_arxiv_id":null,"evidence_quote":"supplies the measured interfacial DMI range around 1.0–1.2 mJ/m2 that the sub-10 nm stability window is compared against."},{"cited_title":"J.: Tunable perpendicular magnetic anisotropy in GdFeCo amorphous films","cited_arxiv_id":null,"evidence_quote":"supplies the perpendicular anisotropy value K≈3×10^4 J/m3 used in the phase diagrams."},{"cited_title":"M., Hessing, P., Churikova, A., Klose, C., Schneider, M., Engel, D., Marcus, C., Bono, D., Bagschik, K., Eisebitt, S., Beach, G","cited_arxiv_id":null,"evidence_quote":"reports experimental 10–30 nm skyrmions in Pt/GdCo/TaOx, the benchmark for the simulated size-versus-DMI relation."},{"cited_title":"M., Zhang, X., Zhou, Y., Ezawa, M., Liu, X., Finizio, S., Raabe, J., Lee, N","cited_arxiv_id":null,"evidence_quote":"provides evidence of reduced skyrmion Hall effect in ferrimagnetic films, supporting the device-motivation part of the claim."}],"review_version":1}