Topological Hall Effect in Antiferromagnetic Co doped Fe$_3$GaTe$_2$

Chanyoung Lee; Gregory T. McCandless; Jeehoon Kim; Jinyoung Yun; Julia Y. Chan; Luis Balicas; Sang-Eon Lee; Shyam Raj Karullithodi; Vadym Kulichenko; W. Kice Brown

arxiv: 2606.21254 · v1 · pith:DOP53DNQnew · submitted 2026-06-19 · ❄️ cond-mat.mes-hall

Topological Hall Effect in Antiferromagnetic Co doped Fe₃GaTe₂

Shyam Raj Karullithodi , Yeonkyu Lee , Vadym Kulichenko , W. Kice Brown , Sang-Eon Lee , Chanyoung Lee , Jinyoung Yun , Gregory T. McCandless

show 3 more authors

Julia Y. Chan Jeehoon Kim Luis Balicas

This is my paper

Pith reviewed 2026-06-26 13:27 UTC · model grok-4.3

classification ❄️ cond-mat.mes-hall

keywords topological Hall effectantiferromagnetic skyrmionsmetamagnetic transitionvan der Waals magnetsFe3GaTe2magnetic force microscopychiral spin texturesCo doping

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The pith

Co doping converts the van der Waals ferromagnet Fe3GaTe2 to an antiferromagnet that develops a topological Hall signal from field-induced chiral spin textures.

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

The work maps how cobalt substitution changes Fe3GaTe2 from a high-temperature ferromagnet into an antiferromagnet whose Neel temperature depends on the cobalt fraction. In the composition near x=0.6 the Hall resistivity follows the magnetization through a metamagnetic transition that erases the antiferromagnetic order. At low temperatures a separate topological Hall contribution appears and peaks at 4 tesla inside the transition field window. Magnetic force microscopy images reveal circular domains 100-200 nm across that form in the antiferromagnetic phase and track the topological Hall resistivity. The authors conclude that the field stabilizes chiral textures, possibly antiferromagnetic skyrmions, which convert to ferromagnetic skyrmions at higher fields.

Core claim

In Fe3-xCoxGaTe2 with x near 0.6 the antiferromagnetic ground state is suppressed by an external field through a metamagnetic transition that produces an anomalous Hall response matching the magnetization curve; at low temperature a distinct topological Hall peak appears at 4 tesla within the transition region, while MFM shows nearly circular domains whose stabilization correlates with the topological Hall signal, indicating that the domains carry chiral character and likely represent antiferromagnetic skyrmions that evolve into ferromagnetic ones with increasing field.

What carries the argument

Metamagnetic transition that induces and stabilizes nearly circular chiral magnetic domains whose presence produces the topological Hall resistivity in the antiferromagnetic phase.

If this is right

The doped compound supplies a platform to track how antiferromagnetically coupled skyrmions convert into ferromagnetic skyrmions under increasing field.
The topological Hall effect serves as an electrical probe for the appearance of these textures during the metamagnetic transition.
Differences between the skyrmion Hall effect in the antiferromagnetic and ferromagnetic regimes can be studied within one material.
The observations suggest that antiferromagnetic skyrmions may already exist in the zero-field antiferromagnetic state before the field is applied.

Where Pith is reading between the lines

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

Analogous doping routes could stabilize skyrmions in other van der Waals antiferromagnets without engineered heterostructures.
If the transition temperatures can be raised, the same material family might support room-temperature studies of skyrmion conversion.
The observed domain diameters indicate textures small enough for high-density spintronic concepts once stability is improved.

Load-bearing premise

The topological Hall resistivity is generated by chiral spin textures such as skyrmions rather than by non-chiral scattering or ordinary domain-wall contributions.

What would settle it

A measurement or calculation showing that the circular domains lack net chirality or that the topological Hall signal survives after the domains are removed would disprove the skyrmion interpretation.

read the original abstract

Fe$_3$GaTe$_2$ is van der Waals (vdW) ferromagnet with a Curie temperature $T_C$ ranging from 350 K to 380 K, followed upon cooling by a ferrimagnetic transition near room temperature. Substituting Fe with Co was previously reported to induce antiferromagnetism (AFM) at a Co fraction dependent Neel temperature $T_N$. In this work, we confirm the overall phase diagram of the Fe$_{3-x}$Co$_x$GaTe$_2$ series as a function of $x$ and temperature via magnetization and electrical transport measurements. For $x \simeq 0.6$ the Hall effect is observed to mimic the magnetization as the AF ground state is suppressed by the external magnetic field via a metamagnetic transition, thus displaying an anomalous Hall response. At low temperatures, we also observe a pronounced topological Hall signal peaking at $\mu_0H$ = 4 T, or within the metamagnetic transition region of fields. This observation points to the presence of magnetic field-induced chiral spin textures, such as skyrmions upon approaching magnetization saturation. Magnetic force microscopy (MFM) reveals the emergence of nearly circular magnetic domains, with diameters on the order of 100 to 200 nm, within the antiferromagnetic phase. A detailed analysis of the MFM images indicates that the topological Hall effect is closely linked to the field-induced stabilization of magnetic domain structures, likely exhibiting chiral textures. This observation suggests the possible formation of skyrmions already in the AFM phase, i.e., AFM skyrmions, that evolve into ferromagnetic (FM) ones upon increasing the magnetic field. Consequently, Co-doped Fe$_3$GaTe$_2$ might provide a platform to investigate the transformation of skyrmions, initially coupled antiferromagnetically into ferromagnetic skyrmions, and to explore its impact on the topological and skyrmion Hall effects.

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 shows a topological Hall peak at the metamagnetic transition in Co-doped Fe3GaTe2 plus MFM circular domains, but the skyrmion assignment stays interpretive.

read the letter

The main takeaway is an experimental report of a topological Hall signal in the antiferromagnetic phase of Fe3-xCoxGaTe2 at x around 0.6. The signal peaks near 4 T where the field drives the metamagnetic transition, and MFM picks up 100-200 nm circular domains that the authors tie to possible AFM skyrmions converting to FM ones.

The work confirms the overall phase diagram with magnetization and transport data and adds the Hall and microscopy pieces for this doping level. The alignment between the transport feature and the MFM domains is the clearest new element; prior literature on the undoped or differently doped compound does not describe this combination.

The measurements themselves appear solid from the abstract description: the Hall resistivity tracks the magnetization in the AFM regime and shows an extra component inside the transition. That consistency is useful for groups studying doped van der Waals magnets.

The soft spot is the step from raw signals to chiral textures. Isolating the topological Hall term requires subtracting ordinary and anomalous contributions, yet the paper does not show that the anomalous coefficient stays constant across the transition. MFM contrast reveals domains but does not establish handedness or nonzero topological charge; no Lorentz TEM or other chirality probe is mentioned. Non-chiral non-collinear scattering near the transition remains a possible alternative.

This is a specialized experimental note for readers already working on skyrmions or topological transport in 2D magnets. It adds one more material platform with concrete numbers and images, even if the skyrmion claim needs tighter evidence. I would send it to referees rather than desk reject; the data are concrete enough to merit community scrutiny.

Referee Report

2 major / 2 minor

Summary. The manuscript reports magnetization, transport, and MFM measurements on Fe_{3-x}Co_x GaTe_2 (x≈0.6), confirming the AFM ground state and its suppression via a metamagnetic transition to FM order. It identifies a pronounced topological Hall resistivity component that peaks at μ0H≈4 T inside the transition at low T, interpreted as arising from field-induced chiral spin textures (skyrmions), with MFM images showing 100-200 nm circular domains in the AFM phase that are taken as evidence for AFM skyrmions evolving into FM skyrmions.

Significance. If the extracted topological Hall signal is shown to originate from real-space Berry curvature of chiral textures rather than alternative scattering mechanisms, the work would identify a vdW platform in which AFM and FM skyrmions can be interconverted by field, enabling studies of the associated topological and skyrmion Hall effects.

major comments (2)

[transport data analysis (Hall resistivity decomposition)] The subtraction procedure used to isolate the topological Hall resistivity (ordinary + anomalous contributions removed) is not shown to remain valid when the anomalous Hall coefficient may vary across the metamagnetic transition; this assumption is load-bearing for the central claim that a distinct topological term exists at μ0H=4 T.
[MFM results and discussion] MFM images display circular domains of 100-200 nm but supply no information on handedness or topological charge (no in-plane sensitivity, vector MFM, or Lorentz TEM is described); the inference that these domains are chiral skyrmions therefore rests on an untested assumption.

minor comments (2)

[title and abstract] Notation for the doping level is inconsistent between title (Fe$_3$GaTe$_2$) and abstract (Fe$_{3-x}$Co$_x$GaTe$_2$); standardize throughout.
[abstract] The temperature at which the topological Hall peak is reported should be stated explicitly in the abstract rather than only as 'low temperatures'.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful and constructive review. We address the two major comments point by point below, proposing textual clarifications and additional analysis where feasible while remaining faithful to the data presented in the manuscript.

read point-by-point responses

Referee: [transport data analysis (Hall resistivity decomposition)] The subtraction procedure used to isolate the topological Hall resistivity (ordinary + anomalous contributions removed) is not shown to remain valid when the anomalous Hall coefficient may vary across the metamagnetic transition; this assumption is load-bearing for the central claim that a distinct topological term exists at μ0H=4 T.

Authors: We acknowledge the concern. The manuscript shows that the Hall resistivity closely tracks the magnetization through the metamagnetic transition, which underpins our assumption that the anomalous Hall coefficient remains approximately constant. To strengthen this, we will expand the methods and results sections with an explicit step-by-step description of the subtraction, including the functional form used for the ordinary and anomalous terms, and add a supplementary figure displaying the raw Hall resistivity, the subtracted ordinary+anomalous background, and the resulting topological component at multiple temperatures across the transition. This will allow readers to assess the robustness of the extracted topological term. revision: yes
Referee: [MFM results and discussion] MFM images display circular domains of 100-200 nm but supply no information on handedness or topological charge (no in-plane sensitivity, vector MFM, or Lorentz TEM is described); the inference that these domains are chiral skyrmions therefore rests on an untested assumption.

Authors: We agree that standard MFM lacks sensitivity to in-plane components and therefore cannot directly establish handedness or topological charge. The manuscript presents the circular domains together with their correlation to the field range where the topological Hall signal appears, and we interpret this combination as consistent with chiral textures. In revision we will modify the discussion to state explicitly that the MFM data provide morphological support but that chirality remains an inference; we will also note that direct confirmation would require vector MFM or Lorentz TEM and suggest these as natural follow-up experiments. No new experimental data can be added at this stage. revision: partial

Circularity Check

0 steps flagged

No circularity: purely experimental report with no derivations or self-referential fits

full rationale

The manuscript is an experimental study reporting magnetization, transport, and MFM data on Fe_{3-x}Co_xGaTe_2. The central observation is a field-dependent Hall resistivity component interpreted as topological Hall effect linked to possible skyrmions, but this rests on standard subtraction of ordinary and anomalous Hall terms plus direct imaging rather than any equation or parameter fit that reduces the reported signal to a quantity defined by the same data. No self-citation chains, uniqueness theorems, or ansatzes are invoked to force the result. The derivation chain is empty; the claims are falsifiable by independent measurements of Hall resistivity and real-space spin textures.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

Experimental condensed-matter study; no free parameters, axioms, or invented entities are introduced beyond standard assumptions of Hall-effect physics and magnetic imaging.

pith-pipeline@v0.9.1-grok · 5942 in / 1195 out tokens · 23277 ms · 2026-06-26T13:27:44.788087+00:00 · methodology

discussion (0)

Reference graph

Works this paper leans on

11 extracted references · 1 canonical work pages

[2]

National High Magnetic Field Laboratory, Tallahassee, Florida 32310, United States
[3]

Department of Physics, Florida State University, Tallahassee, Florida 32306, United States
[4]

Department of Physics, Pohang University of Science and Technology, Pohang 37673, Republic of Korea
[5]

Center for Quantum Dynamics of Angular Momentum, Pohang University of Science and Technology, Pohang 37673, Republic of Korea
[6]

Department of Chemistry & Biochemistry, Baylor University, Waco, Texas 76706, United States
[7]

Figure S1

Department of Physics and Astronomy, Baylor University, Waco, Texas 76706, United States *Correspondence to E-mail: jeehoon@postech.ac.kr; luis_balicas@baylor.edu 43 Methods. Figure S1. Comparison among the lattice parameters of the Fe 3-xCoxGaTe2 series where the nominal concentration (top) is compared to the one obtained from elemental analysis (bottom)...

2016
[8]

The raw MFM frequency-shift image is converted to a grayscale matrix and normalized to the range [0,1]

Normalization and smoothing. The raw MFM frequency-shift image is converted to a grayscale matrix and normalized to the range [0,1]. A mild Gaussian filter (typical kernel σ = 1–2 pixels) is applied to suppress high-frequency noise without altering the overall domain morphology
[9]

bright” and “dark

Binary segmentation and up-domain fraction f↑. An intensity threshold is determined by Otsu’s method, which maximizes the inter- class variance between “bright” and “dark” pixels. Pixels above (below) the threshold are assigned to up (down) domains, yielding a binary map [Fig. 5(b)]. The up-domain area fraction is then computed as f↑ = Nup /(Nup +Ndown), ...
[10]

We apply a Canny edge detector to the smoothed grayscale image to extract the boundaries between bright and dark regions [Fig

Domain -wall extraction and length L DW. We apply a Canny edge detector to the smoothed grayscale image to extract the boundaries between bright and dark regions [Fig. 5(c)]. Small speckles consisting of fewer than Nmin connected pixels (typically Nmin = 10) are removed to avoid counting noise as domain walls. The remaining connected edge pixels form exte...
[11]

Intensity variance. Finally, we compute the variance of the normalized intensity over the entire image, Var(I) = ⟨I2⟩ −⟨I⟩2, which quantifies the overall domain contrast and mixture of bright and 47 dark regions. Each of these metrics is evaluated for all MFM images and plotted as a function of magnetic field in Fig. 5(a)–(c) of the main text. Sweep-direc...

2021
[12]

(2) Casas, B.; Li, Y.; Moon, A.; Xin, Y.; McKeever, C.; Macy, J.; Petford-Long, A.; Phatak, C.; Santos, E.; Choi, E.; et al

DOI: 10.1021/acs.chemrev.0c00297. (2) Casas, B.; Li, Y.; Moon, A.; Xin, Y.; McKeever, C.; Macy, J.; Petford-Long, A.; Phatak, C.; Santos, E.; Choi, E.; et al. Coexistence of Merons with Skyrmions in the Centrosymmetric Van Der Waals Ferromagnet Fe 5-xGeTe2. Adv. Mater. 2023, 35 (17). DOI: 10.1002/adma.202212087. (3) Wu, Y.; Zhang, S.; Zhang, J.; Wang, W.;...

work page doi:10.1021/acs.chemrev.0c00297 2023

[1] [2]

National High Magnetic Field Laboratory, Tallahassee, Florida 32310, United States

[2] [3]

Department of Physics, Florida State University, Tallahassee, Florida 32306, United States

[3] [4]

Department of Physics, Pohang University of Science and Technology, Pohang 37673, Republic of Korea

[4] [5]

Center for Quantum Dynamics of Angular Momentum, Pohang University of Science and Technology, Pohang 37673, Republic of Korea

[5] [6]

Department of Chemistry & Biochemistry, Baylor University, Waco, Texas 76706, United States

[6] [7]

Figure S1

Department of Physics and Astronomy, Baylor University, Waco, Texas 76706, United States *Correspondence to E-mail: jeehoon@postech.ac.kr; luis_balicas@baylor.edu 43 Methods. Figure S1. Comparison among the lattice parameters of the Fe 3-xCoxGaTe2 series where the nominal concentration (top) is compared to the one obtained from elemental analysis (bottom)...

2016

[7] [8]

The raw MFM frequency-shift image is converted to a grayscale matrix and normalized to the range [0,1]

Normalization and smoothing. The raw MFM frequency-shift image is converted to a grayscale matrix and normalized to the range [0,1]. A mild Gaussian filter (typical kernel σ = 1–2 pixels) is applied to suppress high-frequency noise without altering the overall domain morphology

[8] [9]

bright” and “dark

Binary segmentation and up-domain fraction f↑. An intensity threshold is determined by Otsu’s method, which maximizes the inter- class variance between “bright” and “dark” pixels. Pixels above (below) the threshold are assigned to up (down) domains, yielding a binary map [Fig. 5(b)]. The up-domain area fraction is then computed as f↑ = Nup /(Nup +Ndown), ...

[9] [10]

We apply a Canny edge detector to the smoothed grayscale image to extract the boundaries between bright and dark regions [Fig

Domain -wall extraction and length L DW. We apply a Canny edge detector to the smoothed grayscale image to extract the boundaries between bright and dark regions [Fig. 5(c)]. Small speckles consisting of fewer than Nmin connected pixels (typically Nmin = 10) are removed to avoid counting noise as domain walls. The remaining connected edge pixels form exte...

[10] [11]

Intensity variance. Finally, we compute the variance of the normalized intensity over the entire image, Var(I) = ⟨I2⟩ −⟨I⟩2, which quantifies the overall domain contrast and mixture of bright and 47 dark regions. Each of these metrics is evaluated for all MFM images and plotted as a function of magnetic field in Fig. 5(a)–(c) of the main text. Sweep-direc...

2021

[11] [12]

(2) Casas, B.; Li, Y.; Moon, A.; Xin, Y.; McKeever, C.; Macy, J.; Petford-Long, A.; Phatak, C.; Santos, E.; Choi, E.; et al

DOI: 10.1021/acs.chemrev.0c00297. (2) Casas, B.; Li, Y.; Moon, A.; Xin, Y.; McKeever, C.; Macy, J.; Petford-Long, A.; Phatak, C.; Santos, E.; Choi, E.; et al. Coexistence of Merons with Skyrmions in the Centrosymmetric Van Der Waals Ferromagnet Fe 5-xGeTe2. Adv. Mater. 2023, 35 (17). DOI: 10.1002/adma.202212087. (3) Wu, Y.; Zhang, S.; Zhang, J.; Wang, W.;...

work page doi:10.1021/acs.chemrev.0c00297 2023