REVIEW 2 major objections 5 minor 35 references
Magnetic hopfions at room temperature
T0 review · 2 major / 5 minor · reviewed 2026-07-30 · grok-4.5
Pith's one-line read Magnetic hopfions stay stable at room temperature in Co8Zn8Mn4 and form when a bimeron–antibimeron pair fuses.
desk verdict First solid experimental case for long-lived zero-field hopfions at room temperature; TEM–twin identification is the usual soft spot, not a collapse of the claim. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
Bimeron–antibimeron fusion under a helical background, classified by the triplet $(q_t, q_b, h)$ and mapped to Hopf index $H$ via the natural homomorphism; sample thickness of about one helical period ($v \approx 1$) selects a single $H = -1$ hopfion. Energy-minimized micromagnetic digital twins supply the full 3D magnetization used both for Hopf-index evaluation and for simulated Lorentz TEM images matched to experiment.
What would settle it
A direct three-dimensional magnetization reconstruction (for example tomographic Lorentz or X-ray magnetic imaging) of the same laser-written objects that yields Hopf index zero, or that shows the contrast arises from a surface-pinned or through-thickness string rather than a closed bulk hopfion.
Extended reading notes
Core claim
Stable magnetic hopfions with Hopf index $H = -1$ exist in Co8Zn8Mn4 at and above room temperature (roughly 20–320 K). They can be written by single femtosecond laser pulses at zero applied field, exhibit long-lived Brownian-like translational and rotational motion, and form by fusion of a bimeron–antibimeron pair whose mutual orientation matches the surrounding helix. Micromagnetic energy-minimized configurations that reproduce experimental Fresnel contrast, together with the relative homotopy group $\pi_3(S^2, S^2 \setminus \{P_1, P_2\}) = \mathbb{Z}$, underwrite the topological assignment and the formation pathway.
Load-bearing premise
That matching experimental Lorentz TEM contrast to simulated images from energy-minimized micromagnetic models uniquely proves the objects are bulk hopfions with $H = -1$, rather than other three-dimensional or surface-pinned textures that could project similar in-plane magnetization.
Editorial extensions
If this is right
- Room-temperature, zero-field hopfions become an experimental platform for testing proposed Hall effects, racetrack motion, and magnonic focusing.
- Laser fluence and sample thickness can be used as control knobs to select hopfions versus bimeron pairs or composite kπ-like textures.
- Thermally activated collapse near Tc sets a practical upper temperature window (~320 K for long lifetime in this compound).
- Only one mutual orientation of a bimeron–antibimeron pair produces a hopfion; the opposite orientation remains a stable separated pair across thicknesses.
Reading between the lines
- If screw coupling of hopfion translation and rotation is as rigid as claimed, relative orientation of two hopfions could serve as a built-in depth gauge along the helix axis without tomography.
- The strong drop of occurrence probability with composite-texture size suggests laser nucleation statistics track inverse self-energy; that relation could be tested as a design rule for writing more complex bags.
- Extending the same laser-plus-Lorentz protocol to thicker plates (several helical periods) should produce linked hopfions or hopfion rings if the free-surface selection rule is the main reason only H = −1 appears here.
Signed reviews
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The manuscript reports stable magnetic hopfions in the β-Mn-type chiral magnet Co8Zn8Mn4 at and above room temperature (~20–320 K), nucleated at zero field by single femtosecond laser pulses and imaged by Lorentz TEM. Multi-hour sequences show Brownian-like translational/rotational motion; a lifetime-versus-temperature table documents thermally activated collapse near Tc. Combined with micromagnetic digital twins and relative homotopy classification (π3 and the (qt, qb, h) triplet), the authors identify the objects as H = −1 hopfions and argue that they form by fusion of a bimeron–antibimeron pair. A thickness series (106–216 nm) is presented as a static reconstruction of intermediate fusion stages, and occurrence statistics of composite kπ-like and bag-like textures are correlated with inverse self-energies.
Significance. If the identification holds, this is the first experimental realization of magnetic hopfions under ambient conditions, removing the cryogenic constraint that has limited B20-family hopfion work. The combination of in situ laser nucleation, hours-long zero-field stability, a quantitative lifetime table, thickness-tuned intermediate states, and explicit Hopf-index evaluation on simulated twins constitutes a usable experimental platform for transport, magnonics, and information-processing proposals that previously lacked a room-temperature host. The formation pathway via orientation-selective bimeron fusion and the homotopy framing are concrete contributions beyond a pure observation paper.
major comments (2)
- [Hopfion formation through bimeron fusion; Figs. 1–3] Central identification of the observed contrast as bulk hopfions with H = −1 rests on matching Fresnel/TIE images to energy-minimized micromagnetic twins, then computing H on the simulated m(r) (Figs. 1c–d, 2b–d, 3c–d; Eqs. 1–4). Lorentz TEM constrains only the thickness-projected in-plane magnetization. In plates with t ∼ LD the paper itself shows surface-attached states (Fig. 3c) and broken helical periodicity; other 3D or surface-pinned textures can share similar projections. The manuscript should explicitly discuss residual projection degeneracy, state which alternative configurations were energy-minimized and rejected, and clarify how the thickness series and orientation-selective fusion close (or bound) that degeneracy for the H = −1 assignment.
- [Table I; Observation of room-temperature hopfions] Table I reports hopfion lifetimes from at most four independent events per temperature, with lower bounds only at 320 K. The claim of exceptional thermal stability up to ~320 K and rapid collapse above it is load-bearing for “room-temperature hopfions.” The text should quantify uncertainty (e.g., survival analysis or confidence intervals) and state whether collapse is always to the helical background or sometimes to other textures, so that the lifetime trend can be assessed independently of the topological assignment.
minor comments (5)
- [Methods; Magnetic properties of Co8Zn8Mn4] Fig. 1b caption and main text give LD ≈ 140 nm and Ms = 240 kA/m; Methods then set A = 5.8 pJ/m and D = 0.52 mJ/m² so that 4πA/D = 140 nm. Briefly state how A (or the exchange stiffness) was fixed independently of D, or note that only the ratio is constrained by LD.
- [Figures and Methods] Typographical inconsistencies: “Appleid field” in Fig. 1b; “T ransient” and “DA T A A V AILABILITY” spacing artifacts; “over-focuse” in Fig. 4a caption; mixed “cm−2” vs “mJ/cm²” for fluence (text vs Fig. 4).
- [Hopfion formation through bimeron fusion] Eq. (3)–(4) and the map (qt, qb, h) → H = −2v for bimeron fusion are clear for specialists but dense; a short sentence stating the experimental outcome (one H = −1 hopfion per ~LD plate after surface breaking of periodicity) would help non-topology readers.
- [Methods (Micromagnetic simulations)] The FIB-damaged surface layer is modeled as 8 nm with D = 0. A brief sensitivity check (or citation to prior calibration) would strengthen that the hopfion vs surface-attached distinction in Fig. 3 is not an artifact of that choice.
- [Light-induced composite magnetic textures] Occurrence probabilities in Fig. 4g are from 2000 pulses; state whether multiple textures per field of view were counted independently and whether laser-spot inhomogeneity was checked.
Circularity Check
No derivation-by-construction: RT hopfion claim is experimental; self-citations supply standard topology/micromagnetic methods, not forced outputs.
-
self citation load bearing
[Hopfion formation / homotopy paragraphs; Eqs. (1)–(4); Refs. [8], [13]]
"The approach used to compute the Hopf index of magnetic textures embedded in a helical background is described in Ref. [8]. For the experimentally observed hopfion in Fig. 1d and its corresponding digital twin in Fig. 1c, the Hopf index was calculated to be H=−1. ... the classification provided in Ref. [13] ... (qt, qb, h)∈Z3. ... (−1,1,−v)+(1,−1,−v)=(0,0,−2v), which, according to Eq. (4), yields a hopfion state with Hopf index H=−2v."
Identification of observed objects as H=−1 hopfions and the fusion→hopfion pathway are justified by applying the authors’ own prior classification and Hopf-index procedure to simulated twins, not by an independent external measurement of H. This is method self-citation on the interpretive step only; it does not force the experimental lifetime/TEM observations, so it is minor rather than claim-collapsing.
full rationale
The load-bearing chain is experimental Lorentz TEM of long-lived laser-nucleated textures in Co8Zn8Mn4 at ~20–320 K (Fig. 1d, Table I), plus thickness-dependent intermediate states and a directly imaged bimeron–antibimeron fusion event (Figs. 2a, 3). Micromagnetic parameters (Ms, LD → A, D) are fixed from bulk magnetometry and the helical period, then used to build digital twins whose simulated Fresnel/TIE contrast is compared to experiment—standard forward modeling, not a fit that renames the hopfion claim as a prediction. Hopf index H=−1 and the (qt,qb,h) fusion arithmetic are computed on those simulated m(r) fields via relative homotopy (π3 and the triplet classification), citing the authors’ prior methodological papers [8,13]; that is ordinary method reuse, not a uniqueness theorem that forbids alternatives by self-citation alone, and the underlying homotopy groups are textbook mathematics. Occurrence probability vs inverse self-energy (Fig. 4g) is a post-hoc correlation of independently computed energies with counts, not a fitted input called a prediction. Projection non-uniqueness of TEM is a correctness/identification risk, not circularity. Score 1 only for light self-citation load on the interpretive layer; central RT stability result does not reduce to its inputs by construction.
Assumptions & free parameters
free parameters (5)
- Exchange stiffness A =
5.8 pJ/m
- Bulk DMI constant D =
0.52 mJ/m²
- Saturation magnetization Ms =
240 kA/m
- FIB-damaged surface layer thickness with D=0 =
8 nm
- Laser fluence thresholds =
4.8 and 7.7 mJ/cm²
assumptions (4)
- domain assumption Continuum micromagnetic energy with Heisenberg exchange, bulk DMI, Zeeman, and magnetostatic self-energy (Eq. 5) adequately describes Co8Zn8Mn4 plates on the 4 nm mesh scale.
- standard math Isolated hopfions in a helical background are classified by the relative homotopy group π3(S2, S2 \ {P1,P2}) = Z ∋ H, and strings by the triplet (qt, qb, h) ∈ Z³ with the stated homomorphism to (Q, H).
- domain assumption Fresnel Lorentz TEM contrast at ±1 mm defocus, plus TIE phase reconstruction, is sufficient when matched to simulated projections to identify 3D hopfions versus bimeron pairs and kπ-like composites.
- domain assumption Right-handed β-Mn Co8Zn8Mn4 has Tc ≈ 350 K, LD ≈ 140 nm, and hosts a helical ground state at zero field suitable for hopfion embedding.
Cite this review
Pith. "Pith review of Magnetic hopfions at room temperature." pith.science (2026). https://pith.science/paper/WLSFHFKN
@misc{pith2026260726839,
author = {Pith},
title = {Pith review of: Magnetic hopfions at room temperature},
year = {2026},
howpublished = {\url{https://pith.science/paper/WLSFHFKN}},
note = {Machine review of arXiv:2607.26839}
}
read the original abstract
Hopfions are three-dimensional (3D) topological solitons predicted to exist in diverse magnetic systems, yet their practical utility has been largely restricted to cryogenic environments. Here, we overcome this temperature constraint by demonstrating stable magnetic hopfions in the chiral magnet Co8Zn8Mn4 at and above room temperature. Using a transmission electron microscope equipped for in situ optical excitation, we generate magnetic hopfions with femtosecond laser pulses. Long-term observations further reveal Brownian-like motion at room temperature and thermally activated collapse upon approaching the high-temperature regime. Together with micromagnetic simulations and homotopy group analysis, our experimental observations uncover the hopfion formation mechanism through the fusion of bimeron pairs. These findings establish room-temperature magnetic hopfions and provide a framework for their further studies under technologically relevant conditions.
Figures
Figures from the paper (1 more)
Reference graph
Works this paper leans on
-
[1]
Cambridge University Press, New York, 2004
Nicholas Manton and Paul Sutcliffe.Topological Solitons. Cambridge University Press, New York, 2004
2004
-
[2]
F. N. Rybakov, A. B. Borisov, and A. N. Bogdanov. Three-dimensional skyrmion states in thin films of cubic helimagnets.Phys. Rev. B, 87:094424, Mar 2013
2013
-
[3]
Magnetic skyrmion braids.Nature communications, 12(1):5316, 2021
Fengshan Zheng, Filipp N Rybakov, Nikolai S Kise- lev, Dongsheng Song, Andr´ as Kov´ acs, Haifeng Du, Ste- fan Bl¨ ugel, and Rafal E Dunin-Borkowski. Magnetic skyrmion braids.Nature communications, 12(1):5316, 2021
2021
-
[4]
Magnetic skyrmion bundles and their current-driven dynamics.Nature Nanotechnology, 16(10):1086–1091, 2021
Jin Tang, Yaodong Wu, Weiwei Wang, Lingyao Kong, Boyao Lv, Wensen Wei, Jiadong Zang, Mingliang Tian, and Haifeng Du. Magnetic skyrmion bundles and their current-driven dynamics.Nature Nanotechnology, 16(10):1086–1091, 2021. 9
2021
-
[5]
Rybakov, Zhan Wang, Wenli Gao, Shuaishuai Sun, Wentao Wang, Jun Li, Huanfang Tian, Olle Eriksson, Huaixin Yang, Ying Zhang, Nikolai S
Kaixin Zhu, Filipp N. Rybakov, Zhan Wang, Wenli Gao, Shuaishuai Sun, Wentao Wang, Jun Li, Huanfang Tian, Olle Eriksson, Huaixin Yang, Ying Zhang, Nikolai S. Kiselev, Zian Li, and Jianqi Li. Light-induced bimerons in a chiral magnet.NATURE COMMUNICATIONS, 17(1), APR 1 2026
2026
-
[6]
Hopfion rings in a cubic chiral magnet.Na- ture, 623(7988):718–723, 2023
Fengshan Zheng, Nikolai S Kiselev, Filipp N Rybakov, Luyan Yang, Wen Shi, Stefan Bl¨ ugel, and Rafal E Dunin- Borkowski. Hopfion rings in a cubic chiral magnet.Na- ture, 623(7988):718–723, 2023
2023
-
[7]
Elec- trically writing a magnetic heliknoton in a chiral magnet
Long Li, Dongsheng Song, Weiwei Wang, Lingyao Kong, Shuisen Zhang, Ning Wang, Shilei Zhang, Mingliang Tian, Jiadong Zang, Yizhou Liu, and Haifeng Du. Elec- trically writing a magnetic heliknoton in a chiral magnet. NATURE MATERIALS, 25(6), JUN 2026
2026
-
[8]
Kuchkin, Andrii S
Xiaowen Chen, Donghai Yang, Zefang Li, Jiangteng Guo, Haixue Wang, Yue Hu, Vladyslav M. Kuchkin, Andrii S. Savchenko, Huai Zhang, Bei Ding, Zhipeng Hou, Wen Shi, Filipp N. Rybakov, Olle Eriksson, Stefan Blugel, Yu Han, Rafal E. Dunin-Borkowski, Nikolai S. Kiselev, Xuewen Fu, and Fengshan Zheng. Laser-induced nucle- ation of magnetic hopfions.NATURE PHYSIC...
2026
Show all 35 references
-
[9]
Tokunaga, X
Y. Tokunaga, X. Z. Yu, J. S. White, H. M. Rønnow, D. Morikawa, Y. Taguchi, and Y. Tokura. A new class of chiral materials hosting magnetic skyrmions beyond room temperature.Nature Communications, 6(1):7638, Jul 2015
2015
-
[10]
Topological prop- erties and dynamics of magnetic skyrmions.Nature nan- otechnology, 8(12):899–911, 2013
Naoto Nagaosa and Yoshinori Tokura. Topological prop- erties and dynamics of magnetic skyrmions.Nature nan- otechnology, 8(12):899–911, 2013
2013
-
[11]
Cambridge University Press, 2002
Allen Hatcher.Algebraic Topology. Cambridge University Press, 2002
2002
-
[12]
Rybakov, Aleksandr B
Filipp N. Rybakov, Aleksandr B. Borisov, Stefan Bl¨ ugel, and Nikolai S. Kiselev. New type of stable particlelike states in chiral magnets.Phys. Rev. Lett., 115:117201, Sep 2015
2015
-
[13]
Rybakov, Nikolai S
Xiaowen Chen, Dongsheng Song, Filipp N. Rybakov, Nikolai S. Kiselev, Long Li, Wen Shi, Rui Wu, Xuewen Fu, Olle Eriksson, Stefan Blgel, Rafal E. Dunin- Borkowski, Haifeng Du, and Fengshan Zheng. Electric- current-assisted nucleation of zero-field hopfion rings.Ad- vanced Materi...
2026
-
[14]
Topological invariants of vortices, merons, skyrmions, and their combinations in continuous and discrete sys- tems.Physical Review B, 111(13):134417, 2025
Filipp N Rybakov, Olle Eriksson, and Nikolai S Kiselev. Topological invariants of vortices, merons, skyrmions, and their combinations in continuous and discrete sys- tems.Physical Review B, 111(13):134417, 2025
2025
-
[15]
Kiselev, Luyan Yang, Vla- dyslav M
Fengshan Zheng, Nikolai S. Kiselev, Luyan Yang, Vla- dyslav M. Kuchkin, Filipp N. Rybakov, Stefan Bluegel, and Rafal E. Dunin-Borkowski. Skyrmion-antiskyrmion pair creation and annihilation in a cubic chiral magnet. NATURE PHYSICS, 18(8):863+, AUG 2022
2022
-
[16]
Kostrikin and Yuri I
Alexei I. Kostrikin and Yuri I. Manin.Linear Algebra and Geometry. Gordon and Breach Science Publishers, 1997
1997
-
[17]
Bogdanov and A
A. Bogdanov and A. Hubert. The stability of vortex- like structures in uniaxial ferromagnets.J. Magn. Magn. Mater., 195:182, 1999
1999
-
[18]
Direct imaging of a zero-field target skyrmion and its polarity switch in a chiral magnetic nanodisk.Physical review letters, 119(19):197205, 2017
Fengshan Zheng, Hang Li, Shasha Wang, Dongsheng Song, Chiming Jin, Wenshen Wei, Andr´ as Kov´ acs, Ji- adong Zang, Mingliang Tian, Yuheng Zhang, et al. Direct imaging of a zero-field target skyrmion and its polarity switch in a chiral magnetic nanodisk.Physical review letters,...
2017
-
[19]
Room-temperature zero-field kπ-skyrmions and their field-driven evolutions in chiral nanodisks.Nano Letters, 23(22):10205–10212, 2023
Yongsen Zhang, Meng Shi, Weiwei Wang, Xitong Xu, Mingliang Tian, Dongsheng Song, and Haifeng Du. Room-temperature zero-field kπ-skyrmions and their field-driven evolutions in chiral nanodisks.Nano Letters, 23(22):10205–10212, 2023
2023
-
[20]
Chiral magnetic skyrmions with arbitrary topological charge.Physical review B, 99(6):064437, 2019
Filipp N Rybakov and Nikolai S Kiselev. Chiral magnetic skyrmions with arbitrary topological charge.Physical review B, 99(6):064437, 2019
2019
-
[21]
Foster, C
D. Foster, C. Kind, P. J. Ackerman, J. S. B. Tai, M. R. Dennis, and I. I. Smalyukh. Two-dimensional skyrmion bags in liquid crystals and ferromagnets.Nat. Phys., 15:655–659, 2019
2019
-
[22]
Stable skyrmion bundles at room temperature and zero magnetic field in a chiral magnet.Nature Commu- nications, 15(1):3391, 2024
Yongsen Zhang, Jin Tang, Yaodong Wu, Meng Shi, Xi- tong Xu, Shouguo Wang, Mingliang Tian, and Haifeng Du. Stable skyrmion bundles at room temperature and zero magnetic field in a chiral magnet.Nature Commu- nications, 15(1):3391, 2024
2024
-
[23]
Room-temperature creation and conversion of individual skyrmion bags in magnetic multilayered disks.Nature Communications, 16(1):125, 2025
Quan Liu, Shouzhe Dong, Yutong Wang, Junhang Liu, Guofu Xu, Hua Bai, Hao Bai, Weideng Sun, Zhiying Cheng, Yunjie Yan, et al. Room-temperature creation and conversion of individual skyrmion bags in magnetic multilayered disks.Nature Communications, 16(1):125, 2025
2025
-
[24]
Embedded skyrmion bags in thin films of chiral magnets.Advanced materials, 36(36):2403274, 2024
Luyan Yang, Andrii S Savchenko, Fengshan Zheng, Niko- lai S Kiselev, Filipp N Rybakov, Xiaodong Han, Ste- fan Bl¨ ugel, and Rafal E Dunin-Borkowski. Embedded skyrmion bags in thin films of chiral magnets.Advanced materials, 36(36):2403274, 2024
2024
-
[25]
Controlled formation of skyrmion bags.Advanced Materials, page 2501250, 2025
Lisa-Marie Kern, Vladyslav M Kuchkin, Victor Deinhart, Christopher Klose, Themistoklis Sidiropoulos, Maike Auer, Simon Gaebel, Kathinka Gerlinger, Riccardo Bat- tistelli, Steffen Wittrock, et al. Controlled formation of skyrmion bags.Advanced Materials, page 2501250, 2025
2025
-
[26]
X. S. Wang, A. Qaiumzadeh, and A. Brataas. Current- driven dynamics of magnetic hopfions.Phys. Rev. Lett., 123:147203, Sep 2019
2019
-
[27]
Three-dimensional dynamics of a magnetic hop- fion driven by spin transfer torque.Phys
Yizhou Liu, Wentao Hou, Xiufeng Han, and Jiadong Zang. Three-dimensional dynamics of a magnetic hop- fion driven by spin transfer torque.Phys. Rev. Lett., 124:127204, Mar 2020
2020
-
[28]
Troncoso, Vagson L
Carlos Saji, Roberto E. Troncoso, Vagson L. Carvalho- Santos, Dora Altbir, and Alvaro S. Nunez. Hopfion- driven magnonic hall effect and magnonic focusing.Phys. Rev. Lett., 131:166702, Oct 2023
2023
-
[29]
Topological hall signatures of magnetic hop- fions.Phys
B¨ orge G¨ obel, Collins Ashu Akosa, Gen Tatara, and In- grid Mertig. Topological hall signatures of magnetic hop- fions.Phys. Rev. Res., 2:013315, Mar 2020
2020
-
[30]
Magnon scattering modulated by omnidirectional hopfion motion in antiferromagnets for meta-learning.Science Advances, 9(6):eade7439, 2023
Zhizhong Zhang, Kelian Lin, Yue Zhang, Arnaud Bour- nel, Ke Xia, Mathias Kl¨ aui, and Weisheng Zhao. Magnon scattering modulated by omnidirectional hopfion motion in antiferromagnets for meta-learning.Science Advances, 9(6):eade7439, 2023
2023
-
[31]
Waseer, Yunshan Cao, and Peng Yan
Waleed I. Waseer, Yunshan Cao, and Peng Yan. Non- linear dynamics of hopfions for frequency multiplication. Phys. Rev. Appl., Jul 2026
2026
-
[32]
Muratov, Filipp N
Giovanni Di Fratta, Cyrill B. Muratov, Filipp N. Ry- bakov, and Valeriy V. Slastikov. Variational principles of micromagnetics revisited.SIAM Journal on Mathemati- cal Analysis, 52(4):3580–3599, 2020
2020
-
[33]
Magnetic skyrmion braids.Nature Communications, 12(1):5316, 2021
Fengshan Zheng, Filipp N Rybakov, Nikolai S Kise- lev, Dongsheng Song, Andr´ as Kov´ acs, Haifeng Du, Ste- fan Bl¨ ugel, and Rafal E Dunin-Borkowski. Magnetic skyrmion braids.Nature Communications, 12(1):5316, 2021. 10
2021
-
[34]
F. N. Rybakov and E. Babaev. Excalibur software.http: //quantumandclassical.com/excalibur/
-
[35]
Vansteenkiste et al
A. Vansteenkiste et al. The design and verification of MuMax3.AIP Adv., 4:107133, 2014
2014
Reviewed July 30, 2026 · model on record in the stance chip above.
Discussion (0). Continue with ORCID to comment.