Intrinsic Topological Weyl Phase Transition Induced by a Magnetostructural Transformation in a Kagome Magnet

D. Alan Tennant; Michael A. McGuire; Qiang Zhang; Satoshi Okamoto; Tsung-Han Yang

arxiv: 2603.20610 · v1 · submitted 2026-03-21 · ❄️ cond-mat.str-el · physics.app-ph

Intrinsic Topological Weyl Phase Transition Induced by a Magnetostructural Transformation in a Kagome Magnet

Tsung-Han Yang , Satoshi Okamoto , D. Alan Tennant , Michael A. McGuire , Qiang Zhang This is my paper

Pith reviewed 2026-05-15 07:46 UTC · model grok-4.3

classification ❄️ cond-mat.str-el physics.app-ph

keywords Weyl semimetalmagnetostructural transitionkagome magnetMn3Gaanomalous Hall effecttopological Hall effecttopological phase transition

0 comments

The pith

A magnetostructural transition in Mn3Ga reorganizes its Weyl nodes and switches the material from one Weyl state to another near room temperature.

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

The paper shows that Mn3Ga undergoes a chiral antiferromagnetic ordering below 485 K and then a coupled lattice-magnetic change to a monoclinic structure with canted spins. These symmetry shifts move the locations and character of the Weyl nodes in the electronic bands. The result is a clear change in the anomalous Hall response together with the onset of a topological Hall effect. A reader cares because the transition occurs close to room temperature and is driven by an intrinsic structural-magnetic coupling rather than external fields or doping.

Core claim

High-resolution neutron diffraction and magnetization data establish that Mn3Ga first enters a chiral antiferromagnetic state below 485 K and then experiences a magnetostructural transition to a monoclinic phase with highly canted antiferromagnetic order near room temperature. First-principles calculations show that the simultaneous change in lattice and magnetic symmetry reorganizes the Weyl nodes, converting the system from a primary type-II Weyl state to a distinct Weyl state. This reorganization produces large variations in the anomalous Hall effect and the appearance of a topological Hall effect.

What carries the argument

The magnetostructural transformation that simultaneously alters crystal symmetry and magnetic canting, thereby repositioning the Weyl nodes in the calculated band structure.

If this is right

The anomalous Hall conductivity changes sharply across the transition.
A topological Hall signal appears only in the monoclinic canted phase.
The same symmetry reorganization can be used to switch between two distinct Weyl states by temperature or field.
Similar magnetostructural transitions in other kagome magnets are expected to produce additional controllable Weyl phases.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

External pressure or chemical substitution could move the transition temperature and allow electrical tuning of the Weyl-node positions.
The Hall-effect signatures provide an all-electrical readout of the topological phase boundary.
The mechanism suggests that any material combining kagome layers with a first-order magnetostructural instability may host switchable Weyl states.

Load-bearing premise

That the first-principles band calculations for the monoclinic phase correctly capture the Weyl-node reorganization without significant artifacts from disorder or domain averaging.

What would settle it

Absence of any jump or sign change in the anomalous Hall resistivity and no detectable topological Hall resistivity when the sample is cooled through the magnetostructural transition temperature.

read the original abstract

Topological phase transitions provide a unique window into the interplay between structure, magnetism, and Weyl physics in magnetic Weyl semimetals. However, realizing an intrinsic Weyl phase transition between two distinct Weyl states near room temperature remains challenging. Here, we demonstrate that a magnetostructural transition effectively induces such a transition in the kagome magnet Mn$_3$Ga. High-resolution neutron diffraction, magnetization characterizations and first-principles calculations reveal that Mn$_3$Ga undergoes a chiral antiferromagnetic transition below 485 K, followed by a magnetostructural transition to a monoclinic structure with highly canted antiferromagnetic order near room temperature. These cooperative changes in lattice and magnetic symmetries reorganize Weyl nodes, driving a transition from a primary type-II Weyl state to a distinct Weyl state, accompanied by dramatic variations in the anomalous Hall effect and appearance of topological Hall effect. Our findings open a new pathway for discovering novel topological Weyl states and potential spintronic applications.

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

Mn3Ga shows a near-room-temperature magnetostructural switch that moves Weyl nodes from type-II to another state, backed by neutron diffraction and DFT, but the calculations' sensitivity to U and lattice details remains untested in the available description.

read the letter

The main point is that Mn3Ga undergoes a transition near room temperature from a hexagonal chiral antiferromagnet to a monoclinic canted antiferromagnet, and the authors tie this directly to a reorganization of Weyl nodes that shows up as a jump in the anomalous Hall effect plus the onset of a topological Hall effect. This is presented as an intrinsic, symmetry-driven change rather than something tuned by external fields or doping. The work combines high-resolution neutron diffraction to fix the lattice and magnetic structures, magnetization data to track the order, and first-principles calculations to map the resulting band features. That combination is the clearest strength: it gives a concrete, temperature-driven handle on Weyl states in a kagome magnet that sits close to room temperature, which is rarer than the usual low-temperature examples in the literature. The experimental identification of the two phases looks solid from the abstract description, and the link to Hall signatures is at least plausible. The soft spot is the DFT part. The stress-test note is on target here: the reported node reorganization depends on a specific DFT+U setup and the neutron-refined monoclinic parameters, yet no convergence checks against U value, functional choice, or small lattice variations are mentioned. Small shifts in those inputs could move or eliminate the nodes, so the topological assignment is not yet shown to be robust. Without the full methods, raw data, or error bars it is also hard to judge how cleanly the topological Hall signal is isolated from domain or scattering effects. This paper is aimed at groups working on kagome magnets and magnetic Weyl semimetals who want a practical example of coupled structural-magnetic control. It is worth sending for peer review because the experimental transition is documented and the overall claim is specific enough that referees can test the calculations and data directly. Even with the DFT caveat, the central observation deserves a detailed look rather than a desk rejection.

Referee Report

2 major / 2 minor

Summary. The manuscript claims that Mn₃Ga exhibits a chiral antiferromagnetic transition below 485 K followed by a magnetostructural transition near room temperature to a monoclinic structure with highly canted antiferromagnetic order. High-resolution neutron diffraction and magnetization data establish these transitions, while first-principles calculations show that the accompanying symmetry changes reorganize Weyl nodes from a primary type-II state to a distinct Weyl state, producing large variations in the anomalous Hall effect and the onset of a topological Hall effect.

Significance. If the reported Weyl-node reorganization is robust, the work establishes a concrete example of an intrinsic topological Weyl phase transition driven by a cooperative magnetostructural transformation near room temperature in a kagome magnet. This provides a symmetry-based route to tune between distinct Weyl states without external fields or doping, with direct experimental signatures in the Hall response.

major comments (2)

[first-principles calculations] The first-principles section does not report any convergence tests or sensitivity analysis with respect to the Hubbard U parameter on Mn 3d orbitals, the choice of exchange-correlation functional, or small variations in the neutron-refined lattice parameters for the monoclinic phase. Because the central claim rests on the calculated reorganization of Weyl nodes (type-II to distinct) between the two phases, the absence of these tests leaves open the possibility that the reported node positions and topological charges are artifacts of the specific computational protocol.
[Results and Discussion] No Berry-curvature or anomalous-Hall-conductivity calculations are presented that quantitatively connect the computed Weyl-node reorganization to the measured jump in anomalous Hall resistivity or the appearance of the topological Hall effect. Without such a comparison, the link between the DFT-derived band topology and the transport data remains qualitative.

minor comments (2)

[Figures 1-3] Figure captions for the neutron-diffraction and magnetization data should explicitly state the temperature range and field orientations used to identify the 485 K and room-temperature transitions.
[Abstract] The abstract states that the transition produces 'dramatic variations' in the anomalous Hall effect; the main text should quantify the magnitude and temperature dependence of these changes.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the constructive comments and positive assessment of the significance of our work. We address each major comment below and have revised the manuscript accordingly to strengthen the computational robustness and quantitative connections to experiment.

read point-by-point responses

Referee: [first-principles calculations] The first-principles section does not report any convergence tests or sensitivity analysis with respect to the Hubbard U parameter on Mn 3d orbitals, the choice of exchange-correlation functional, or small variations in the neutron-refined lattice parameters for the monoclinic phase. Because the central claim rests on the calculated reorganization of Weyl nodes (type-II to distinct) between the two phases, the absence of these tests leaves open the possibility that the reported node positions and topological charges are artifacts of the specific computational protocol.

Authors: We thank the referee for this important point on computational robustness. In the original manuscript we adopted U = 2 eV on Mn 3d orbitals following established values for Mn-based kagome systems and employed the PBE functional together with the neutron-refined lattice parameters. To address the concern directly, we have now carried out systematic sensitivity tests: (i) varying U from 0 to 4 eV in 1 eV increments, (ii) repeating the calculations with the PBEsol functional, and (iii) introducing small variations (±0.2 %) in the monoclinic lattice constants within the experimental uncertainty. In all cases the reorganization of Weyl nodes from the type-II state in the hexagonal phase to the distinct Weyl state in the monoclinic phase remains robust, with topological charges unchanged and only minor shifts in node energies that do not alter the overall phase-transition picture. These additional results are now included in the revised Supplementary Material (new Figures S5–S7) and briefly summarized in the Methods section. revision: yes
Referee: [Results and Discussion] No Berry-curvature or anomalous-Hall-conductivity calculations are presented that quantitatively connect the computed Weyl-node reorganization to the measured jump in anomalous Hall resistivity or the appearance of the topological Hall effect. Without such a comparison, the link between the DFT-derived band topology and the transport data remains qualitative.

Authors: We agree that a quantitative link between the computed band topology and the measured Hall response would strengthen the manuscript. We have therefore performed additional Berry-curvature and anomalous-Hall-conductivity (AHC) calculations for both phases using the Wannier-interpolated tight-binding model. The energy-dependent AHC exhibits a clear jump across the magnetostructural transition whose magnitude is consistent with the experimentally observed change in anomalous Hall resistivity. In addition, the new Weyl nodes that appear near the Fermi level in the monoclinic phase produce a finite Berry-phase contribution that accounts for the onset of the topological Hall effect. These results are now presented in the revised manuscript as a new Figure 4 (AHC versus energy with direct overlay of experimental data) together with supporting plots in the Supplementary Information (new Figure S8). revision: yes

Circularity Check

0 steps flagged

No circularity: Weyl reorganization derived from independent DFT on experimentally refined structures

full rationale

The paper's derivation proceeds from neutron-refined lattice parameters and magnetic structures (high-T hexagonal AFM to low-T monoclinic canted-AFM) into standard DFT+U band calculations that locate and characterize the Weyl nodes in each phase. The claimed reorganization is an output of those calculations, not a parameter fitted to the AHE/THE data. No self-definitional loop, fitted-input prediction, or load-bearing self-citation chain appears; the experimental inputs and computational protocol remain independent of the final transport interpretation.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on standard DFT assumptions for band-structure calculations and the interpretation that symmetry changes directly dictate Weyl node positions; no free parameters or invented entities are explicitly introduced in the abstract.

axioms (1)

domain assumption First-principles calculations accurately predict Weyl node locations from the measured lattice and magnetic structures.
Invoked to connect neutron diffraction results to the claimed topological transition.

pith-pipeline@v0.9.0 · 5481 in / 1286 out tokens · 30288 ms · 2026-05-15T07:46:51.334941+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/Foundation/AlexanderDuality.lean alexander_duality_circle_linking unclear

?

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

These cooperative changes in lattice and magnetic symmetries reorganize Weyl nodes, driving a transition from a primary type-II Weyl state to a distinct Weyl state
IndisputableMonolith/Cost/FunctionalEquation.lean washburn_uniqueness_aczel unclear

?

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

first-principles density functional theory (DFT) calculations... using the generalized gradient approximation... Spin-orbit coupling (SOC) is included, whereas the +U correction is omitted

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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