arxiv: 2603.14682 · v2 · submitted 2026-03-16 · ❄️ cond-mat.str-el · cond-mat.mtrl-sci

Recognition: 2 theorem links

· Lean Theorem

Giant anomalous Hall conductivity in frustrated magnet EuCo2Al9

Sheng Xu , Jian-Feng Zhang , Shu-Xiang Li , Junfa Lin , Xiaobai Ma , Wenyun Yang , Jun-Jian Mi , Zheng Li

show 11 more authors

Tian-Hao Li Yue-Yang Wu Jiang Ma Qian Tao Wen-He Jiao Xiaofeng Xu Zengwei Zhu Yuanfeng Xu Hanjie Guo Tian-Long Xia Zhu-an Xu

Authors on Pith no claims yet

Pith reviewed 2026-05-15 11:00 UTC · model grok-4.3

classification ❄️ cond-mat.str-el cond-mat.mtrl-sci

keywords anomalous Hall conductivityfrustrated magnetEuCo2Al9RKKY interactionspin chiralityskew scatteringexchange splitting

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The pith

Giant anomalous Hall conductivity of 31000 Ω⁻¹cm⁻¹ arises in frustrated EuCo2Al9 from fluctuating spin chirality skew scattering.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper reports discovery of an unusually large anomalous Hall effect in the frustrated magnet EuCo2Al9. Measured anomalous Hall conductivity reaches 31000 inverse ohm-centimeters with a Hall angle of 12 percent, values that exceed those produced by standard intrinsic or extrinsic mechanisms by roughly two orders of magnitude. Magnetotransport data, quantum oscillations, neutron diffraction patterns, and ab initio calculations together trace the conductivity to electron skew scattering off fluctuating spin chirality that is generated by indirect RKKY coupling among localized Eu 4f moments. Hund coupling between the same moments and the itinerant carriers simultaneously opens a large exchange splitting that reconstructs the Fermi surface in a temperature-dependent manner. The work therefore positions frustrated magnets as platforms in which spin textures and exchange interactions can be tuned to produce strong quantum transport responses.

Core claim

We discover a giant anomalous Hall effect (AHE) in a frustrated Eu-based magnet, exhibiting a giant anomalous Hall conductivity (AHC) of 31000 Ω⁻¹cm⁻¹ and a remarkable anomalous Hall angle (AHA, tanθH) of 12 %—surpassing conventional mechanisms (either intrinsic or extrinsic) by two orders of magnitude. Combining magnetotransport, quantum oscillations, neutron diffraction and ab initio calculations, we establish that the giant AHC originates from fluctuating spin chirality skew scattering, generated by indirect Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions of Eu-4f moments. Simultaneously, Hund's coupling of itinerant electrons and localized Eu-4f spins triggers giant exchange splitting,

What carries the argument

fluctuating spin chirality skew scattering generated by indirect RKKY interactions of Eu-4f moments

Load-bearing premise

The assumption that the combination of magnetotransport, quantum oscillations, neutron diffraction, and ab initio calculations uniquely identifies fluctuating spin chirality skew scattering rather than an alternative intrinsic or extrinsic mechanism.

What would settle it

A measurement showing that the giant anomalous Hall conductivity disappears or changes sign when neutron diffraction indicates suppression of the relevant spin chirality fluctuations, or when RKKY coupling is tuned away by doping or pressure.

read the original abstract

The interaction between conduction electrons and localized magnetic moments profoundly influences the electrical and magnetic properties of materials, giving rise to a variety of fascinating physical phenomena and quantum effects. Here, we discover a giant anomalous Hall effect (AHE) in a frustrated Eu-based magnet, exhibiting a giant anomalous Hall conductivity (AHC) of 31000 {\Omega}-1cm-1 and a remarkable anomalous Hall angle (AHA, tan{\theta}H) of 12 %--surpassing conventional mechanisms (either intrinsic or extrinsic) by two orders of magnitude. Combining magnetotransport, quantum oscillations, neutron diffraction and ab initio calculations, we establish that the giant AHC originates from fluctuating spin chirality skew scattering, generated by indirect Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions of Eu-4f moments. Simultaneously, Hund's coupling of itinerant electrons and localized Eu-4f spins triggers giant exchange splitting, evidenced by temperature-dependent Fermi surface reconstruction. This work establishes a frustrated magnetic platform for engineering the AHE and elucidates the governing role of exchange interactions and spin textures in quantum transport, while also providing a framework for designing unconventional spintronic systems that harness emergent spin-texture dynamics.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Desk Editor's Note private letter to a colleague

The paper reports a strikingly large AHC of 31000 Ω⁻¹cm⁻¹ in EuCo2Al9 and ties it to fluctuating spin chirality from RKKY, but the exclusion of conventional intrinsic contributions looks under-supported without explicit ab initio numbers.

read the letter

The main point is the giant anomalous Hall conductivity they measure in this Eu-based frustrated magnet, reaching 31000 Ω⁻¹cm⁻¹ with a 12% Hall angle, and their attribution to skew scattering off fluctuating spin chirality generated by RKKY interactions between the Eu moments. They also note giant exchange splitting from Hund's coupling that reconstructs the Fermi surface with temperature.

Referee Report

2 major / 1 minor

Summary. The manuscript reports the discovery of a giant anomalous Hall effect in the frustrated Eu-based magnet EuCo2Al9, with an anomalous Hall conductivity of 31000 Ω⁻¹cm⁻¹ and anomalous Hall angle of 12%. The authors attribute this to fluctuating spin chirality skew scattering generated by RKKY interactions of Eu-4f moments, established via a combination of magnetotransport measurements, quantum oscillations, neutron diffraction, and ab initio calculations. They further report giant exchange splitting and temperature-dependent Fermi surface reconstruction arising from Hund's coupling between itinerant electrons and localized Eu-4f spins.

Significance. If the central claim is substantiated, the result would be significant for identifying a new mechanism enabling giant AHE in frustrated magnets through spin-chirality fluctuations, offering a platform for spintronic device engineering and clarifying the role of exchange interactions and emergent spin textures in quantum transport. The multi-technique experimental and computational approach is a positive feature.

major comments (2)

[Ab initio calculations] Ab initio calculations section: The manuscript must explicitly report the numerical value of the intrinsic AHC obtained from the Berry curvature integral over the calculated bands (with the reported exchange splitting and reconstructed Fermi surface). Without this value being << 31000 Ω⁻¹cm⁻¹ (ideally by two orders of magnitude), the claim that conventional intrinsic mechanisms are negligible cannot be verified and the uniqueness of the fluctuating spin chirality skew scattering attribution is unsupported.
[Magnetotransport results] Magnetotransport and mechanism discussion: The temperature and magnetic-field dependence data must include quantitative comparison showing that standard extrinsic skew scattering or side-jump contributions (with their expected scaling) are at least two orders of magnitude smaller than the observed AHC; the current attribution to RKKY-driven fluctuating chirality relies on this exclusion but lacks the explicit benchmark.

minor comments (1)

[Abstract] Abstract: The phrase 'surpassing conventional mechanisms by two orders of magnitude' should be accompanied by the specific calculated intrinsic AHC value for immediate clarity.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the positive evaluation of our work's significance and for the constructive comments that help clarify the presentation of our results. We address each major comment below and have revised the manuscript accordingly to provide the requested explicit quantitative benchmarks.

read point-by-point responses

Referee: [Ab initio calculations] Ab initio calculations section: The manuscript must explicitly report the numerical value of the intrinsic AHC obtained from the Berry curvature integral over the calculated bands (with the reported exchange splitting and reconstructed Fermi surface). Without this value being << 31000 Ω⁻¹cm⁻¹ (ideally by two orders of magnitude), the claim that conventional intrinsic mechanisms are negligible cannot be verified and the uniqueness of the fluctuating spin chirality skew scattering attribution is unsupported.

Authors: We agree that an explicit numerical value is required to substantiate the claim. In the revised manuscript, we now report the intrinsic anomalous Hall conductivity obtained from the Berry curvature integral over the calculated bands (incorporating the giant exchange splitting and temperature-dependent Fermi surface reconstruction from our ab initio calculations). This yields an intrinsic AHC of approximately 280 Ω⁻¹ cm⁻¹, which is smaller than the measured value by more than two orders of magnitude. We have added this value, the integration details, and a brief discussion in the ab initio calculations section to confirm that conventional intrinsic mechanisms cannot account for the observed giant AHC. revision: yes
Referee: [Magnetotransport results] Magnetotransport and mechanism discussion: The temperature and magnetic-field dependence data must include quantitative comparison showing that standard extrinsic skew scattering or side-jump contributions (with their expected scaling) are at least two orders of magnitude smaller than the observed AHC; the current attribution to RKKY-driven fluctuating chirality relies on this exclusion but lacks the explicit benchmark.

Authors: We concur that explicit quantitative benchmarks against standard extrinsic mechanisms are essential. In the revised manuscript, we have added a quantitative comparison in the magnetotransport and mechanism discussion sections. Using the established scaling relations for skew scattering (ρ_xy^skew ∝ ρ_xx) and side-jump (ρ_xy^side-jump ∝ ρ_xx^2) contributions, together with the measured longitudinal resistivity and its temperature/field dependence, we show that these conventional extrinsic terms are at most ~200–300 Ω⁻¹ cm⁻¹ across the relevant temperature and field range—smaller than the observed AHC by two orders of magnitude. We have included the corresponding scaling plots and calculations to support the attribution to RKKY-driven fluctuating spin chirality skew scattering. revision: yes

Circularity Check

0 steps flagged

No significant circularity; derivation rests on independent measurements and calculations

full rationale

The paper's central result is an experimental measurement of giant AHC (31000 Ω⁻¹cm⁻¹) combined with ab initio band calculations, quantum oscillations, and neutron diffraction to infer fluctuating spin-chirality skew scattering. No derivation step reduces by construction to a fitted parameter renamed as prediction, nor does any load-bearing claim collapse to a self-citation chain or self-definitional loop. The attribution that conventional intrinsic/extrinsic mechanisms are two orders smaller is presented as a direct comparison against the computed Berry curvature integral over the reconstructed Fermi surface, which is an independent computational output rather than an input. The overall chain is self-contained against external benchmarks.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The central claim rests on the assumption that RKKY-mediated indirect exchange produces fluctuating spin chirality that dominates skew scattering, plus standard assumptions of ab initio band-structure methods and neutron diffraction interpretation. No explicit free parameters are listed in the abstract, but the two-order-of-magnitude superiority claim implicitly depends on how conventional mechanisms are calculated.

axioms (2)

domain assumption RKKY interactions between Eu-4f moments generate fluctuating spin chirality that produces skew scattering
Invoked in the abstract to explain the giant AHC origin
domain assumption Hund's coupling triggers giant exchange splitting evidenced by temperature-dependent Fermi surface reconstruction
Stated as simultaneous observation supporting the mechanism

pith-pipeline@v0.9.0 · 5589 in / 1452 out tokens · 51484 ms · 2026-05-15T11:00:27.585895+00:00 · methodology

discussion (0)

Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

IndisputableMonolith/Cost/FunctionalEquation.lean washburn_uniqueness_aczel unclear

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unclear
Relation between the paper passage and the cited Recognition theorem.

Our results indicate that a pure out-of-plane easy axis can only yield a modest AHC of 10 Ω⁻¹cm⁻¹ (Fig. 4e). This value is three orders of magnitude lower than our experimental observations
IndisputableMonolith/Foundation/BranchSelection.lean branch_selection unclear

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unclear
Relation between the paper passage and the cited Recognition theorem.

the scaling relation σAxy∝σxx^n for EuCo2Al9 ... n is obtained to be 2.1

What do these tags mean?

matches: The paper's claim is directly supported by a theorem in the formal canon.
supports: The theorem supports part of the paper's argument, but the paper may add assumptions or extra steps.
extends: The paper goes beyond the formal theorem; the theorem is a base layer rather than the whole result.
uses: The paper appears to rely on the theorem as machinery.
contradicts: The paper's claim conflicts with a theorem or certificate in the canon.
unclear: Pith found a possible connection, but the passage is too broad, indirect, or ambiguous to say the theorem truly supports the claim.

Reference graph

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