{"id":"dee0d613-e381-4b74-9ed8-5f9b788580d3","arxiv_id":"2607.15844","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":0,"one_line_summary":"Joule heating reversibly drives a spin-reorientation transition from out-of-plane to in-plane magnetization in Co/Fe3GaTe2 heterostructures at about 311 K and in an 80–100 mW power window.","lead":"A Co/Fe3GaTe2 magnetic sandwich switches its preferred magnetization direction from out-of-plane to in-plane when heated, and the same switch happens when a small electric current heats the device. The result points toward heat-assisted electrical control of van der Waals magnets without large write currents.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"The SRT claim rests on interpreting composite MOKE loops as exchange-driven Co reorientation; without element-resolved data, the same evolution could arise from FGaT dominating the polar Kerr signal while Co stays in-plane.","rationale":"I agree with the reader's weakest-assumption identification. The central claim is explicitly about an exchange-mediated anisotropy competition, so proving that the Co layer's magnetization direction changes is necessary. Without element-resolved data, the MOKE evolution is compatible with a signal-weighting scenario in which FGaT remains the main polar Kerr source and Co stays in-plane. The paper's internal evidence—reversible cycles, Co-free controls, IP-loop complementarity, STM growth showing direct interfacial contact—makes the SRT plausible and is honestly discussed; I do not see an internal inconsistency or a demonstrated error. The weaknesses are missing measurements, not contradictions. For that reason the appropriate outcome is the same CONDITIONAL verdict, with the acceptance condition being element-resolved confirmation of Co reorientation (and ideally a measured device temperature). An XMCD experiment as a function of temperature through TR on the same stack would settle the question.","tokens_in":16811,"tokens_out":6725,"duration_ms":70579,"concrete_test":"Perform element-resolved X-ray magnetic circular dichroism (XMCD) hysteresis loops at the Co L3 and Fe L3 edges on the same Pd/Co/FGaT stack as a function of temperature through TR≈311 K (and, if possible, on the device as a function of input power), extracting OOP and IP projections of Co and Fe separately. If Co OOP remanence is ≈1 at 297 K and collapses while Fe remains ferromagnetically ordered near 311 K, the exchange-mediated SRT is confirmed. If Co remains in-plane at all temperatures while the Fe signal weakens, the apparent transition is a MOKE weighting artifact. A fallback using existing apparatus: measure temperature-dependent polar Kerr loops of a Co-free FGaT flake of the same thickness on the same heating stage; if it remains square with large Mr/Ms at 311–340 K, the Co/FGaT crossover cannot be explained by FGaT losing PMA alone.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The load-bearing step is the inference that the square OOP loop at 297.5 K arises because the Co layer is exchange-rotated out of plane, so that the OOP-to-IP evolution is a genuine spin reorientation of the heterostructure. The alternative—FGaT dominating the polar Kerr signal while Co stays in-plane at all temperatures—can reproduce the data: the OOP loop would be a square FGaT loop plus a linear Co background, and heating would make it progressively harder-axis-like as FGaT approaches its Curie temperature; the observed single-step switching would then simply be the FGaT layer switching alone. The paper's counterarguments are suggestive but indirect. '10 nm Co cannot be square alone' does not identify which layer produces the squareness when the signal is not element-resolved. The Co-free controls were measured on different devices with no measured local temperature, so they cannot rule out a higher local temperature in the Co/FGaT stack at the same power. The XAS stability check was performed on a different Pd/[Co/Pd] multilayer on bulk FGaT, not on the Co/FGaT bilayer. The IP-loop complement (low remanence at 297 K, square at 374 K) is the strongest existing evidence for coupling, but it is still a composite optical measurement. Therefore the central claim that Co reorients remains inferred; the paper itself lists XMCD as future work.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The manuscript investigates Co/Fe3GaTe2 (FGaT) heterostructures and reports a temperature- and Joule-heating-driven transition from an out-of-plane (OOP) to an in-plane (IP) dominated magnetic state. The authors measure polar and longitudinal MOKE hysteresis loops as a function of temperature (297–377 K) and electrical power (0–254 mW), finding that the OOP loop evolves from square with Mr/Ms≈1 to hard-axis-like, while the IP loop becomes more square; the nucleation-field zero crossing defines TR≈311 K. In a device, OOP remanence collapses in an 80–100 mW window and is reversible over five cycles. Co-free FGaT devices retain square OOP loops to much higher power, and Kerr microscopy shows power-thresholded field-assisted reversal near 15 mW. In situ STM shows Co grows as clusters on the Te-terminated surface. The authors interpret the results as an exchange-mediated anisotropy competition in which weakening FGaT anisotropy allows Co's IP shape anisotropy to dominate. They explicitly discuss and argue against the alternative that the effect is merely a change in Kerr signal weighting.","tokens_in":17092,"tokens_out":6522,"duration_ms":56134,"significance":"If correct, this is a valuable demonstration of electrothermal anisotropy control in a room-temperature vdW ferromagnet heterostructure, with potential relevance to heat-assisted writing. The manuscript's strengths include complementary OOP/IP MOKE data, reversible cycling, Co-free controls, direct domain imaging of nucleation, and in situ STM of the interface. The central difficulty is that the key inference—that the Co layer rotates out of plane at low temperature—is drawn from composite optical signals, not element-resolved measurements. The paper's own proposed future XMCD experiment is the natural arbiter. Until such data (or an equivalent decisive experiment) are provided, the SRT interpretation remains plausible but not proven.","major_comments":[{"comment":"The central claim of a genuine SRT rests on the inference that the square OOP loop at 297.5 K arises because exchange rotates the 10 nm Co layer out of plane. The alternative—FGaT dominating polar Kerr while Co stays in-plane—can reproduce the OOP evolution (square at low T, hard-axis near TC) and single-step switching. The counterarguments are indirect: the 10 nm Co argument does not identify the source of squareness without element resolution; Co-free controls are on different devices without local temperature; XAS stability was on Pd/[Co/Pd]/bulk FGaT. The IP complement is the strongest evidence but remains composite. The manuscript itself lists XMCD as future work. This gap is load-bearing for the title/abstract claim. Please add element-resolved data or a decisive thickness experiment, or temper the conclusion.","section":"§3, Discussion (paragraph beginning 'Two scenarios...')"},{"comment":"The statement that Co-free controls 'confirm that the crossover in the heterostructure is not set by the loss of FGaT ferromagnetism alone' is not fully supported. The control devices have different FGaT thicknesses (28.8 nm vs ~100 nm) and no measured local temperature; the dissipated power is a proxy, and the Co/FGaT stack may reach a different local temperature at the same P. The 80–100 mW window and TR≈311 K are compared only qualitatively (the paper acknowledges this). A thickness-matched control with thermal modeling or direct local temperature measurement would strengthen the argument.","section":"§3, Co-free control paragraph"}],"minor_comments":[{"comment":"Typo: 'an useful platform' should be 'a useful platform'.","section":"Sec. 1"},{"comment":"Typo: 'tansition' should be 'transition'. Also, the caption could explicitly state that the coils represent the FGaT and Co layers for clarity.","section":"Fig. 3(b) caption"},{"comment":"The XAS stability check was performed on Pd(3 nm)/[Co(0.3 nm)/Pd(0.8 nm)]10/Pd(3 nm) grown on bulk FGaT, not on the Co/FGaT bilayer used for the SRT measurements. Clarify in the main text that this is a 'related' heterostructure and discuss any possible differences in interface reactivity.","section":"Sec. 3, XAS paragraph"},{"comment":"The label 'Left:' is confusing because the schematic appears above the panels; consider revising to 'Top left' or 'Schematic'.","section":"Fig. 4 caption"}],"recommendation":"major_revision","confidential_remarks":"The paper is within scope and the experimental dataset is rich. The main concern is the gap between the data and the SRT interpretation. I do not think rejection is warranted; the authors have anticipated the key alternative and provided reasonable, if not conclusive, counterarguments. A revision that provides element-resolved or thickness-dependent evidence, or that clearly reframes the conclusions as inferred, would be sufficient."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"This paper is worth reading and worth refereeing, but the central claim is not yet fully proven. What's new here is a device-level, reversible thermal and electrothermal crossover from out-of-plane to in-plane dominated magnetism in a Co/Fe3GaTe2 bilayer, with a reorientation temperature around 311 K and an electrothermal window near 80–100 mW. That is a genuinely useful addition to the 2D-magnet manipulation literature.\n\nThe experiments are well executed. Temperature- and power-dependent MOKE loops in both geometries, nucleation-field sign reversal, remanence ratios, reversibility over five cycles, Co-free control devices, and Kerr microscopy of power-thresholded reversal all hang together coherently. The authors also explicitly confront the main alternative explanation—signal weighting rather than true reorientation—and give three arguments against it. The Co-free controls and the IP-loop complement are sensible, and the paper does not oversell: it openly states that device temperature was not measured and lists XMCD as future work. That honesty counts.\n\nThe soft spot is exactly what the reader flagged. All magnetic data are composite magneto-optical signals; there is no element-resolved measurement. The alternative scenario—FGaT dominates the polar Kerr signal while Co stays in-plane—can reproduce the qualitative loop evolution as FGaT weakens near its Curie temperature. The counterarguments (10 nm Co cannot be square alone; single-step switching) are suggestive but indirect. They do not identify which layer contributes the squareness when the signal mixes both layers. The Co-free control devices were not measured at the same local temperature as the Co/FGaT device, so they cannot fully rule out a different thermal profile. The XAS stability check was done on a different stack, so it supports chemical robustness only loosely. These are addressable gaps, not demonstrated errors.\n\nMissing error bars on extracted coercivities and remanence ratios also limit quantitative comparison, but that is a fixable presentational issue.\n\nThe citation pattern looks appropriate: relevant prior work on FGaT anisotropy, torque switching, cAFM writing, and exchange-transferred reorientation is cited. The paper does not overclaim novelty beyond the specific Co/FGaT SRT result.\n\nFor peer review: yes, send it. It deserves referee time. The experimental phenomenology is solid and the question is well posed. Ask the authors for element-resolved magnetic data (XMCD) and better thermal calibration; if those confirm the exchange-rotation picture, this becomes a nice contribution. If not, the phenomenology alone still stands as a useful empirical result.","headline":"A credible experimental demonstration of thermal and electrothermal anisotropy crossover in Co/FGaT, but the claim of an exchange-driven spin reorientation needs element-resolved proof before it fully lands.","tokens_in":17810,"tokens_out":1481,"would_cite":true,"duration_ms":18310,"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":"Heating reversibly flips the easy axis of a Co/Fe3GaTe2 heterostructure between perpendicular and in-plane, near 311 K.","keywords":["spin-reorientation transition","Fe3GaTe2","van der Waals magnet","cobalt heterostructure","Joule heating","magnetic anisotropy","magneto-optical Kerr effect","electrothermal control"],"falsifier":"Measure element-specific magnetization (e.g., X-ray magnetic circular dichroism at the Co and Fe absorption edges) while sweeping temperature through the transition. If the cobalt layer is found to remain in-plane at all temperatures while the Fe signal vanishes near 311 K, the apparent spin reorientation is only a change in which layer contributes to the Kerr signal, not a physical rotation of the heterostructure's magnetization.","tokens_in":16690,"feed_emoji":"🧲","tokens_out":6672,"duration_ms":55822,"temperature":0.7,"pith_summary":"This paper claims that in a bilayer of a conventional cobalt film and the van der Waals ferromagnet Fe3GaTe2, the overall magnetic easy axis can be reversibly switched between perpendicular and in-plane by heating, either externally or through the Joule heat of an applied current. The switch occurs near 311 K, well below the Curie temperature, because the cobalt layer's in-plane preference gains dominance as Fe3GaTe2's perpendicular anisotropy weakens. The authors demonstrate the same reorientation in a working device within an 80–100 mW electrical power window, reversible over multiple cycles, and a cobalt-free control shows that heating alone lowers the domain-nucleation barrier, enabling field-assisted writing near a 15 mW threshold. This yields an electrothermal handle for controlling magnetism in two-dimensional spintronic devices without large write currents.","feed_headline":"Joule heating flips magnetic easy axis in Co/Fe3GaTe2","feed_subtitle":"A cobalt layer and a van der Waals magnet trade dominance near room temperature, enabling power-controlled magnetic switching.","key_machinery":"The central mechanism is the spin-reorientation transition (SRT), a temperature-driven crossover of the easy axis controlled by competing anisotropy terms. Here the competition is between the strong perpendicular magnetic anisotropy (PMA) of the van der Waals ferromagnet Fe3GaTe2 and the in-plane shape anisotropy of the cobalt overlayer, with interfacial exchange coupling acting as the mediator that transmits the FGaT anisotropy to the Co layer. The authors define the reorientation temperature T_R operationally as the point where the positive and negative nucleation fields cross zero, which marks the loss of the remanent out-of-plane state. In the device, Joule heating downstream of a leaky","core_discovery":"In a Pd/Co/Fe3GaTe2 heterostructure, the dominant magnetic anisotropy switches from out-of-plane to in-plane when the temperature rises through a reorientation transition near 311 K; the same switch can be driven electrically by Joule heating at 80–100 mW. The mechanism is an exchange-mediated anisotropy competition: at low temperature, interfacial exchange from the strongly perpendicular Fe3GaTe2 layer pulls the cobalt magnetization out of plane, but heating weakens Fe3GaTe2's anisotropy so the cobalt's intrinsic in-plane preference wins. Complementary out-of-plane and in-plane Kerr loops, a zero crossing of the nucleation fields at the transition, and a cobalt-free control showing only bar","pith_inferences":["The anisotropy-competition picture should generalize to other metallic ferromagnets on van der Waals magnets, with the reorientation temperature set by the ratio of the two anisotropies; a testable prediction is that thicker cobalt layers shift T_R upward.","The power-thresholded switching at a fixed assist field is the operating principle of heat-assisted magnetic recording, so this geometry could be a platform for low-energy writing if pulsed excitation reduces the required energy below the quasi-static values reported here.","The combination of the tunable nucleation barrier with the defect-induced Dzyaloshinskii-Moriya interactions seen in the same crystals suggests a route to writing skyrmion or bubble textures on demand, though that remains to be demonstrated.","If the apparent reorientation is a true rotation of the cobalt layer, element-resolved probes should see the cobalt moment tilt continuously across the transition; the paper leaves this as explicit future work."],"forward_implications":["A single device can reversibly toggle between out-of-plane- and in-plane-dominated magnetic states using electrical power alone, without changing material or stoichiometry.","The transition occurs at a power threshold rather than a field threshold, so moderate applied fields can write a magnetic state when combined with heating.","Because the reorientation happens about 40–70 K below the Curie point, the switching works while the van der Waals magnet remains ferromagnetic, preserving its useful properties.","In a cobalt-free control, the same electrothermal softening lowers the reversal field by roughly a factor of five, enabling power-thresholded field-assisted reversal near 15 mW.","The effect is reversible over at least five thermal and electrical cycles, with no detectable chemical change between the metal and the van der Waals layer."],"fun_headline_variants":["Heat flips magnet's easy axis in Co/Fe3GaTe2","Joule heating steers magnetic order in vdW heterostructure","Power-controlled magnetic switching in Co/Fe3GaTe2","Electrothermal reorientation at 311 K in Co/FGaT","Heat and electricity toggle magnet's axis in Co/Fe3GaTe2"],"cache_read_input_tokens":2304,"weakest_assumption_plain":"The interpretation that the square out-of-plane hysteresis loop at room temperature arises because interfacial exchange coupling rotates the cobalt layer's magnetization out of plane, rather than because the Fe3GaTe2 layer alone dominates the magneto-optical signal within the optical penetration depth.","fun_headline_variants_meta":{"raw":{"variants":["Heat flips magnet's easy axis in Co/Fe3GaTe2","Joule heating steers magnetic order in vdW heterostructure","Power-controlled magnetic switching in Co/Fe3GaTe2","Electrothermal reorientation at 311 K in Co/FGaT","Heat and electricity toggle magnet's axis in Co/Fe3GaTe2"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000868,"raw_usage":{"total_tokens":3610,"prompt_tokens":767,"completion_tokens":2843,"prompt_tokens_details":{"cached_tokens":256},"prompt_cache_hit_tokens":256,"prompt_cache_miss_tokens":511,"completion_tokens_details":{"reasoning_tokens":2757}},"tokens_in":511,"tokens_out":2843,"duration_ms":17399,"temperature":1.0,"reasoning_tokens":2757,"cache_read_input_tokens":256,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-01T22:07:39.825818+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure element-specific magnetization (e.g., X-ray magnetic circular dichroism at the Co and Fe absorption edges) while sweeping temperature through the transition. If the cobalt layer is found to remain in-plane at all temperatures while the Fe signal vanishes near 311 K, the apparent spin reorientation is only a change in which layer contributes to the Kerr signal, not a physical rotation of the heterostructure's magnetization.","supporting_citations":[],"review_version":1}