Magnetic Entropy in a Non-Collinear Weak Ferromagnetic YCrO3

Ambesh Dixit; Brajesh Tiwari; M. S. Ramachandra Rao

REVIEW 4 major objections 5 minor 10 references

Magnetic Entropy in a Non-Collinear Weak Ferromagnetic YCrO3

T0 review · 4 major / 5 minor · reviewed 2026-08-14 · deepseek-v4-flash

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Pith's one-line read The paper finds that YCrO3's magnetic entropy drops by 0.38 joules per kilogram per kelvin at 8 tesla around 140 K, and that the low-field curvature in magnetization is a fingerprint of weak ferromagnetism.

desk verdict A plausible new MCE data point for YCrO3, but the missing error bars, unsupported mean-field fit, and placeholder references make the central entropy claim provisional. read the letter →

arxiv 1908.06454 v1 pith:MNFQSXGS submitted 2019-08-18 cond-mat.str-el cond-mat.mtrl-sci

Brajesh Tiwari , Ambesh Dixit , M. S. Ramachandra Rao This is my paper · ORCID

classification cond-mat.str-elcond-mat.mtrl-sci

keywords weakferromagnetismYCrO3magneticentropymagnetocaloriceffectantiferromagnetictransitionDzyaloshinskii-MoriyainteractioncantedG-typeantiferromagnetMaxwellrelation

verification ladder T0 review T1 audit T2 compute T3 formal

The pith

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

The reading

The paper tries to establish that the magnetic entropy of the weak ferromagnet YCrO3 changes by about $-0.38\,\mathrm{J\,kg^{-1}\,K^{-1}}$ at an applied field of 8 T, with the largest change appearing just before the Cr$^{3+}$ antiferromagnetic ordering at 140 K. It argues that this entropy change is larger than a purely collinear antiferromagnet would produce, and that the extra contribution comes from the canted, non-collinear spin arrangement generated by the Dzyaloshinskii–Moriya interaction. The evidence is the nonlinear magnetization response below 3 T, which the authors interpret as the signature of weak ferromagnetism, together with linear response at higher fields where a mean-field description works. If the interpretation is right, magnetocaloric measurements can serve as a sensitive probe of weak ferromagnetism in this family of distorted perovskite chromites.

What carries the argument

The central objects are the canted G-type antiferromagnetic spin arrangement of Cr$^{3+}$ moments and the Maxwell relation $(\partial S/\partial H)_T = \mu_0(\partial M/\partial T)_H$, integrated over isothermal magnetization data to obtain $\Delta S(T,\Delta H) = \mu_0\int (\partial M/\partial T)_H\,dH$. The non-collinearity is described by the Dzyaloshinskii–Moriya interaction $D_{ij}\cdot(\mathbf{S}_i\times\mathbf{S}_j)$, which arises from spin-orbit coupling in the tilted CrO$_6$ octahedra with Cr-O-Cr angles near 147–149 degrees. The canting converts part of the antiferromagnetic response into a weak ferromagnetic moment, which is what the low-field nonlinearity is taken to reveal.

What would settle it

Measure magnetization isotherms on a single crystal of YCrO3 while recording the full hysteresis loop at each temperature, and compare the Maxwell-relation entropy change with the entropy change obtained from field-dependent heat-capacity measurements. If the low-field nonlinearity below 3 T does not disappear when hysteresis is removed, or if the same nonlinearity appears above 140 K in a phase-pure sample, the paper's attribution of the entropy anomaly to intrinsic weak ferromagnetism is not supported.

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Extended reading notes

Core claim

The central claim is that YCrO3, an orthorhombic perovskite with Pnma symmetry, develops canted G-type antiferromagnetic order below about 140 K, and the canting gives rise to weak ferromagnetism through the Dzyaloshinskii–Moriya interaction. From magnetization isotherms and the thermodynamic Maxwell relation, the authors obtain a maximum magnetic-entropy change of approximately $-0.38\,\mathrm{J\,kg^{-1}\,K^{-1}}$ at 8 T, peaking at the ordering temperature. The magnetization is nonlinear up to roughly 3 T and linear from 3 to 8 T, with the entropy change following mean-field behavior at higher fields; the low-field deviation is the paper's evidence for weak ferromagnetism. The conclusion is that the measured entropy change exceeds what a pure collinear antiferromagnet would give, reflecting the non-collinear spin structure.

Load-bearing premise

The entropy change is obtained by integrating magnetization isotherms of a polycrystalline sample assumed to be single-phase, stoichiometric YCrO3 with reversible field response; if a ferromagnetic impurity or magnetic hysteresis contributes to those isotherms, the Maxwell-relation integration would overstate the intrinsic entropy change and weaken the weak-ferromagnetism attribution.

Editorial extensions

If this is right

Near 140 K, YCrO3 will exhibit a magnetocaloric response whose magnitude grows with applied field, reaching about $0.38\,\mathrm{J\,kg^{-1}\,K^{-1}}$ at 8 T.
The field dependence of the peak entropy change splits into two regimes: nonlinear below about 3 T, governed by the weak-ferromagnetic canting, and linear above 3 T, where mean-field behavior applies.
Magnetization isotherms analyzed through the Maxwell relation can locate the onset of weak ferromagnetism in canted antiferromagnets even when the net moment is small.
The entropy anomaly at the transition includes a contribution from field-driven response of the canted moments rather than being purely the antiferromagnetic ordering entropy.
The reported entropy change provides a quantitative benchmark for comparing weak-ferromagnetic contributions across the rare-earth orthochromite series.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

Following the paper's logic, one could test whether the peak $|\Delta S|$ across the ACrO$_3$ family scales with the Cr-O-Cr octahedral tilt angle, which would connect the magnetocaloric response directly to the strength of the Dzyaloshinskii–Moriya interaction.
A direct measurement of the entropy change by field-dependent heat-capacity measurements near 140 K would settle whether the Maxwell-relation value is inflated by magnetic hysteresis or by a trace ferromagnetic impurity in the polycrystalline sample.
The same low-field nonlinearity could be examined through field-cooled and zero-field-cooled magnetization curves: if the nonlinearity persists above the Néel temperature in a phase-pure sample, it would indicate an extrinsic ferromagnetic contribution rather than intrinsic canting.

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Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Desk Editor's Note

read the letter

The one genuinely new thing here is the measured ΔS(T,H) for YCrO3 near 140 K. As far as I can tell, that curve isn't in the prior literature, and the maximum of about -0.38 J/kg K at 8 T is a useful data point for people working on orthochromite magnetocalorics. The method is standard—Maxwell integration of magnetization isotherms—and the low-field nonlinearity they attribute to weak ferromagnetism is qualitatively consistent with what else is known about this material. So the paper is not circular and not nonsense.

That said, the paper is thin in places that matter. The biggest issue is reversibility. The authors themselves note that YCrO3 shows hysteresis in low fields below TN, but they never show whether the isotherms used for the Maxwell integration are single-valued. If the low-field region is irreversible, the computed ΔS could mix in hysteresis losses, and the reported magnitude—even its sign near the peak—could be off. A simple field-up/field-down comparison would settle this, and they should have done it.

Second, the mean-field agreement is asserted, not demonstrated. No equation, no fit parameters, no residuals. As a reader, I can't check that claim, and it's doing real work in their argument that the high-field behavior is understood while the low-field deviation comes from weak ferromagnetism. Without the fit details, that interpretation is suggestive at best.

Third, the references are a mess. Refs 3–7 are obvious placeholder entries from a template—'Title of Chapter' in 'Classic Physiques' is not a real citation. That's careless, and it raises doubts about how much scrutiny the rest of the manuscript got. It's easy to fix, but it needs fixing.

There's also a minor overreach in the conclusion: saying the entropy change is 'relatively larger than expected for pure antiferromagnetic system' has no quantitative basis in the paper.

Overall, the core measurement is plausible and probably valid, but the paper as written doesn't supply enough evidence to trust the central number. It's the kind of result that deserves a serious referee—not a desk reject—because with revision it could be a legitimate, citable characterization. But I wouldn't cite it in its current form.

The right call is to send to peer review with major revisions: show the M(H) data with reversibility check, add error bars, give the mean-field fit or drop the claim, and replace the placeholder references.

Referee Report

4 major / 5 minor

Summary. The paper reports temperature- and field-dependent magnetization measurements on polycrystalline YCrO3, focusing on the magnetic entropy change near the Cr3+ antiferromagnetic ordering temperature of about 140 K. Using the thermodynamic Maxwell relation, the authors compute the isothermal magnetic entropy change ΔS from magnetization isotherms and report a maximum of approximately -0.38 J kg^-1 K^-1 at an 8 T field, occurring just before the magnetic ordering. They interpret the low-field (below 3 T) nonlinearity of the isotherms as evidence of weak ferromagnetism arising from the canted G-type antiferromagnetic structure, and they state that the maximum entropy change fits a mean-field approximation at higher fields, while deviations at lower fields substantiate the weak-ferromagnetism onset.

Significance. If fully documented, the result would provide a quantitative magnetocaloric characterization of YCrO3 near its Néel temperature and would support the view that the weak-ferromagnetic canting contributes to the magnetic entropy change in rare-earth orthochromites. A strength of the paper is that the central entropy value is computed directly from measured magnetization via a standard Maxwell relation rather than from a fitted model, so the main result is not circular. However, the significance is currently limited by missing data display, the absence of error analysis, an undocumented mean-field comparison, and unresolved questions about the reversibility of the magnetization isotherms. The work would be more convincing if the isotherms and entropy curves were shown with defined measurement protocols and uncertainty estimates.

major comments (4)

[Results and Discussion, Fig. 2(a)] The entropy change is obtained by numerical Maxwell integration over H from 0 to 8 T, but the manuscript itself states that YCrO3 shows the onset of hysteresis in low-field magnetic hysteresis measurements below the antiferromagnetic transition temperature of about 140 K, citing references [8,10]. The low-field region below 3 T is precisely where the isotherms are nonlinear and where the authors locate the weak-ferromagnetism signature. If the measured isotherms include irreversible domain or canting reorientation, the derivative (∂M/∂T)_H and the subsequent field integral no longer represent a single-valued equilibrium thermodynamic quantity, so the reported -0.38 J kg^-1 K^-1 cannot be regarded as an intrinsic equilibrium entropy change. The authors should report the field-history protocol in detail, compare ascending and descending branches of the isotherms, and ideally cross-check the entropy change with heat-capacity data, which would also constrain the sign and magnitude of the peak.
[Abstract and Results and Discussion] The abstract claims that the maximum entropy change 'fits well with mean field approximation at higher fields', but the main text provides no mean-field equation, no explicit comparison, no fit parameters, and no residuals. The only quantitative statement in the text is that the magnetization is linear for fields from 3 T to 8 T, which is not the same as demonstrating that the entropy change follows a mean-field prediction. Without a documented mean-field calculation, the attribution of the low-field deviation to weak ferromagnetism remains an interpretation rather than a tested quantitative conclusion. The authors should provide the mean-field expression used, the fitted parameter values (e.g., the effective exchange constant or saturation field), and a measure of the agreement such as residuals over the 3-8 T range.
[Figure captions and data availability] The supplied manuscript contains only figure captions; the actual magnetization isotherms and entropy curves are not visible in the text. The central quantitative claim of this paper rests entirely on these two figures, and no numerical tabulation of M(T,H) or ΔS is provided. The absence of visible data makes it impossible for the reader to verify the field and temperature ranges, the density of isotherms, the quality of the interpolation used for the derivative, or the location of the claimed maximum. The authors must include the actual figures with axis labels, error bars, and a statement of how the numerical derivative and integration were performed. They should also give estimates of the propagated uncertainty in ΔS from the magnetization measurement noise.
[Low-field nonlinearity and phase purity] The low-field nonlinearity is used as evidence of weak ferromagnetism, but the manuscript does not demonstrate that the sample is single-phase and stoichiometric YCrO3, nor does it exclude a ferromagnetic impurity phase such as CrO2 or metallic Cr. A small ferromagnetic impurity contribution would produce nonlinear M(H) at low fields and could inflate the Maxwell-relation entropy change. The paper cites an earlier publication [1] for structural details, but the phase-purity evidence should be summarized here or the relevant powder X-ray diffraction pattern and magnetization-versus-temperature data in low fields should be shown to support the single-phase assumption.

minor comments (5)

[Introduction] There is a typo in the definition of the DM interaction: 'where Si is the spint vector' should read 'where Si is the spin vector'.
[Results and Discussion] The word 'antiferromagetnic' appears instead of 'antiferromagnetic' in the sentence describing temperature-dependent magnetic measurements.
[References] References [3]–[7] appear to be placeholder template entries (for example, 'Classic Physiques' and 'Load-cycling in cubic press') and are not cited in the text. These should be replaced with actual literature relevant to the magnetocaloric effect, Maxwell-relation analysis, and YCrO3 magnetism, or deleted.
[Equation for Maxwell relation] The thermodynamic Maxwell relation is written as (∂S/∂T)_H = (∂M/∂T)_H without a μ0 factor in the first form, while the integrated form includes μ0. For consistency in SI units, either both forms should include μ0 or the relation should be written for the entropy per unit volume with μ0 included explicitly in the magnetic work term.
[Abstract and Conclusion] The temporal location of the maximum entropy change is stated differently in places: the abstract says 'just before magnetic ordering', while the main text says the evolution occurs 'near magnetic phase transition at about 140 K'. Since the isotherms were recorded in 5 K intervals, the authors should state the actual measured temperature of the maximum and clarify whether the peak occurs exactly at the Néel temperature or at a temperature slightly lower.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: the entropy change is computed from measured magnetization isotherms via the Maxwell relation, not from any fitted parameter or self-citation.

full rationale

The paper's central quantitative claim, a magnetic entropy change of about -0.38 J kg^-1 K^-1 at 8 T, is obtained by numerical Maxwell-relation integration of measured M(T,H) isotherms. This is a direct thermodynamic reduction of measured data, not a fitted parameter renamed as a prediction. The brief statement that the maximum entropy change 'fits well with mean field approximation at higher fields' is anecdotal and post hoc rather than the source of the numerical value. Likewise, the weak-ferromagnetism attribution is a qualitative interpretation of low-field nonlinearity in the same measured isotherms, not a consequence derived from a self-imposed ansatz. The manuscript cites the authors' previous work [1] for synthesis, structure, and Neel temperature, but these facts enter only as background characterization and are not used to force the entropy result. The possible concern that magnetic hysteresis or irreversibility could contaminate the Maxwell integration is a measurement-validity issue, not a circularity issue: it does not make the reported value equivalent to its inputs by construction. No load-bearing step reduces to the claim being made, so the circularity score is 0.

Assumptions & free parameters 1 free parameters · 3 assumptions · 0 invented entities

The central ΔS value relies on the Maxwell relation, the standard protocol for magnetocaloric characterization, plus the sample-quality assumption. The DM interaction is a conventional explanation, not a new postulate. No new particles or forces are introduced. The mean-field fit parameters are not reported, which is a transparency gap rather than an additional assumption needed for the entropy computation.

free parameters (1)

Mean-field fit parameters = not reported
The abstract and conclusion assert that the high-field entropy change follows mean-field theory, but no equation or fitted constants are shown. If the fit was used to support the weak-ferromagnetism interpretation, its parameters are a free input.

assumptions (3)

standard math Maxwell relation for isothermal magnetic entropy change is applicable to the measured M(T,H) data.
The derivation of ΔS relies on the thermodynamic identity (dS/dH)_T = μ0 (dM/dT)_H, invoked in the Results section.
domain assumption Dzyaloshinskii-Moriya interaction explains the canted spin structure and weak ferromagnetism in YCrO3.
The paper attributes the low-field nonlinearity to DM-driven non-collinearity, following refs [1,9,10], without direct microscopic evidence.
domain assumption The YCrO3 sample is single-phase, stoichiometric, and free of magnetic impurity phases.
Phase purity is only asserted via previous work [1]; no diffraction pattern or impurity analysis is shown in this manuscript.

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Cite this review

Pith. "Pith review of Magnetic Entropy in a Non-Collinear Weak Ferromagnetic YCrO3." pith.science (2026). https://pith.science/paper/MNFQSXGS

@misc{pith2026190806454,
  author       = {Pith},
  title        = {Pith review of: Magnetic Entropy in a Non-Collinear Weak Ferromagnetic YCrO3},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/MNFQSXGS}},
  note         = {Machine review of arXiv:1908.06454}
}

read the original abstract

We carried out temperature and field dependent magnetic measurements to understand the evolution of magnetic non-collinearity near antiferromagnetic phase in conjunction with the evolution of magnetic entropy near phase transition. We observed the maximum change in entropy just before magnetic ordering of Cr3+ in YCrO3 with the maximum change in magnetic entropy of -0.38 Jkg-1K-1 at 8 Tesla external field. The data is linear in higher fields 3 T - 8 T , whereas it showed deviations in the lower field region. The maximum entropy change fits well with mean field approximation at higher fields, while the observed deviation in lower field substantiates the onset of weak ferromagnetism in YCrO3.

Figures

Figures reproduced from arXiv: 1908.06454 by the authors.

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

10 extracted references · 10 canonical work pages

[1]

Tiwari, M

B. Tiwari, M. K. Surendra, M. S. Ramachandra Rao, HoCrO 3 and YCrO 3: a comparative study, J. Phys.: Condens. Matter 25, 216004 (2013)

work page 2013
[2]

Lyubina, M

J. Lyubina, M. D. Kuzmin, K. Nenkov O. Gutfleisch, M. Richter, D. L. Schlagel, T. A. Lograsso, K. A. Gschneidner Jr, Magnetic field dependence of the maximum magnetic entropy change, Phys. Rev. B, 83, 012403 (2011)

work page 2011
[3]

M. P. Brown and K. Austin, Appl. Phys. Letters 85, 2503–2504 (2004)

work page 2004
[4]

Title of Chapter,

R. T. Wang, “Title of Chapter,” in Classic Physiques , edited by R. B. Hamil (Publisher Name, Publisher City, 1999), pp. 212–213

work page 1999
[5]

Load -cycling in cubic press,

C. D. Smith and E. F. Jones, “Load -cycling in cubic press,” in Shock Compression of Condensed Matter-2001, AIP Conference Proceedings 620, edited by M. D. Furnish et al. (American Institute of Physics, Melville, NY, 2002), pp. 651–654

work page 2001
[6]

B. R. Jackson and T. Pitman, U.S. Patent No. 6,345,224 (8 July 2004)

work page 2004
[7]

Recovery effects in binary aluminum alloys,

D. L. Davids, “Recovery effects in binary aluminum alloys,” Ph.D. thesis, Harvard University, 1998

work page 1998
[8]

Weak ferromagnetism of YCrO 3

V. M. Judin and A. B. Sherman “Weak ferromagnetism of YCrO 3” Solid State Comm. 4, 661-663 (1966)

work page 1966

Show all 10 references

[9]

Phonons and magnetic excitation correlations in weak ferromagnetic YCrO3

Y. Sharma et.al “Phonons and magnetic excitation correlations in weak ferromagnetic YCrO3” Journal of Applied Physics 115, 183907 (2014)

2014
[10]

Alvarez, M

C. Alvarez, M. P. Cruz, A. C. Duran, H. Montiel, R. Zamorano, Weak ferromagnetism in the magnetoelectric YCrO3 detected by microwave power absorption measurements, Solid State Communication, 150, 1597-1600 (2010)

2010

Pith tools

Reviewed August 14, 2026 · model on record in the stance chip above.

[1] [1]

Tiwari, M

B. Tiwari, M. K. Surendra, M. S. Ramachandra Rao, HoCrO 3 and YCrO 3: a comparative study, J. Phys.: Condens. Matter 25, 216004 (2013)

work page 2013

[2] [2]

Lyubina, M

J. Lyubina, M. D. Kuzmin, K. Nenkov O. Gutfleisch, M. Richter, D. L. Schlagel, T. A. Lograsso, K. A. Gschneidner Jr, Magnetic field dependence of the maximum magnetic entropy change, Phys. Rev. B, 83, 012403 (2011)

work page 2011

[3] [3]

M. P. Brown and K. Austin, Appl. Phys. Letters 85, 2503–2504 (2004)

work page 2004

[4] [4]

Title of Chapter,

R. T. Wang, “Title of Chapter,” in Classic Physiques , edited by R. B. Hamil (Publisher Name, Publisher City, 1999), pp. 212–213

work page 1999

[5] [5]

Load -cycling in cubic press,

C. D. Smith and E. F. Jones, “Load -cycling in cubic press,” in Shock Compression of Condensed Matter-2001, AIP Conference Proceedings 620, edited by M. D. Furnish et al. (American Institute of Physics, Melville, NY, 2002), pp. 651–654

work page 2001

[6] [6]

B. R. Jackson and T. Pitman, U.S. Patent No. 6,345,224 (8 July 2004)

work page 2004

[7] [7]

Recovery effects in binary aluminum alloys,

D. L. Davids, “Recovery effects in binary aluminum alloys,” Ph.D. thesis, Harvard University, 1998

work page 1998

[8] [8]

Weak ferromagnetism of YCrO 3

V. M. Judin and A. B. Sherman “Weak ferromagnetism of YCrO 3” Solid State Comm. 4, 661-663 (1966)

work page 1966