Magnetic structure and magnetoelastic coupling of GdNiSi3 and TbNiSi3

C. W. Galdino; D. Rigitano; E. Granado; F. R. Arantes; M. A. Avila; R. Tartaglia; U. F. Kaneko

arxiv: 1907.09830 · v1 · pith:7JAVWCOPnew · submitted 2019-07-23 · ❄️ cond-mat.str-el

Magnetic structure and magnetoelastic coupling of GdNiSi3 and TbNiSi3

R. Tartaglia , F. R. Arantes , C. W. Galdino , D. Rigitano , U. F. Kaneko , M. A. Avila , E. Granado This is my paper

Pith reviewed 2026-05-24 17:17 UTC · model grok-4.3

classification ❄️ cond-mat.str-el

keywords magnetic structurerare-earth intermetallicsresonant x-ray diffractionmagnetoelastic couplingantiferromagnetic stackingGdNiSi3TbNiSi3

0 comments

The pith

GdNiSi3 and TbNiSi3 adopt the same magnetic structure with +-+- stacking of ferromagnetic ac planes and moments along a, reversing the interplane coupling sign seen in YbNiSi3.

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

This paper uses resonant x-ray magnetic diffraction on single crystals to determine the zero-field magnetic structures of GdNiSi3 and TbNiSi3 below their Néel temperatures. Both compounds share the magnetic space group Cmmm', featuring ferromagnetic ac planes stacked antiferromagnetically in a +-+- pattern with rare-earth moments aligned along a. This structure differs from the +--+ stacking and b-axis moment direction reported for YbNiSi3, showing a reversal in the sign of the coupling between second-neighbor R planes. The b-axis lattice parameter expands magnetoelastically below TN, leading to the conclusion that the +-+- pattern is favored under lattice expansion. Competition between stacking patterns of similar energy, tuned by rare-earth size, underlies the magnetic instability observed across the RNiSi3 series.

Core claim

The magnetic structure is the same for GdNiSi3 and TbNiSi3 (magnetic space group Cmmm') and consists of ferromagnetic ac planes stacked in an antiferromagnetic +-+- pattern with moments along a; this indicates a sign reversal of the coupling constant between second-neighbor R planes relative to YbNiSi3, and the long b lattice parameter expands upon cooling below TN, pointing to stabilization of the +-+- stacking under lattice expansion.

What carries the argument

The +-+- antiferromagnetic stacking pattern of ferromagnetic ac planes (magnetic space group Cmmm'), which distinguishes the structure from YbNiSi3 and links the observed b-axis magnetoelastic expansion to the choice of stacking.

If this is right

The coupling constant between second-neighbor R planes reverses sign when the rare-earth changes from Gd or Tb to Yb.
The +-+- stacking pattern is stabilized specifically under b-axis lattice expansion.
Competition between distinct magnetic stacking patterns with similar exchange energies, tuned by rare-earth size, produces the observed magnetic ground-state instability along the series.
Metamagnetic transitions under applied field in some RNiSi3 compounds arise from this near-degeneracy of stacking patterns.

Where Pith is reading between the lines

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

Applying pressure to expand or contract the b axis could switch the preferred stacking pattern in a single compound.
The magnetoelastic expansion may provide a route to tune the magnetic order by controlling lattice parameters independently of rare-earth substitution.
Similar competitions between stacking patterns may appear in other rare-earth intermetallic series where lattice size varies.

Load-bearing premise

The b-axis lattice expansion upon cooling is the dominant selector of the +-+- stacking pattern rather than a secondary effect or other rare-earth-dependent exchange terms.

What would settle it

A direct measurement of the magnetic stacking pattern in an intermediate rare-earth member of the series or under hydrostatic pressure that alters the b lattice parameter without changing the rare-earth ion.

Figures

Figures reproduced from arXiv: 1907.09830 by C. W. Galdino, D. Rigitano, E. Granado, F. R. Arantes, M. A. Avila, R. Tartaglia, U. F. Kaneko.

**Figure 3.** Figure 3: FIG. 3: Temperature-dependence of the integrated intensity [PITH_FULL_IMAGE:figures/full_fig_p003_3.png] view at source ↗

**Figure 2.** Figure 2: FIG. 2: (a) Temperature-dependence of the integrated inten [PITH_FULL_IMAGE:figures/full_fig_p003_2.png] view at source ↗

**Figure 4.** Figure 4: FIG. 4: Temperature-dependence of [PITH_FULL_IMAGE:figures/full_fig_p004_4.png] view at source ↗

**Figure 5.** Figure 5: FIG. 5: Temperature-dependence of [PITH_FULL_IMAGE:figures/full_fig_p005_5.png] view at source ↗

read the original abstract

The series of intermetallic compounds $R$NiSi$_3$ ($R$ = rare earth) shows interesting magnetic properties evolving with $R$ and metamagnetic transitions under applied magnetic field for some of the compounds. The microscopic magnetic structures must be determined to rationalize such rich behavior. Here, resonant x-ray magnetic diffraction experiments are performed on single crystals of GdNiSi$_{3}$ and TbNiSi$_{3}$ at zero field. The primitive magnetic unit cell matches the chemical cell below the N\'eel temperatures $T_{N}$ = 22.2 and 33.2 K, respectively. The magnetic structure is determined to be the same for both compounds (magnetic space group $Cmmm'$). It features ferromagnetic {\it ac} planes that are stacked in an antiferromagnetic $+-+-$ pattern, with the rare-earth magnetic moments pointing along the $\vec{a}$ direction, which contrasts with the $+--+$ stacking and moment direction along the $\vec{b}$ axis previously reported for YbNiSi$_3$. This indicates a sign reversal of the coupling constant between second-neighbor $R$ planes as $R$ is varied from Gd and Tb to Yb. The long {\it b} lattice parameter of GdNiSi$_{3}$ and TbNiSi$_{3}$ shows a magnetoelastic expansion upon cooling below $T_N$, pointing to the conclusion that the $+-+-$ stacking is stabilized under lattice expansion. A competition between distinct magnetic stacking patterns with similar exchange energies tuned by the size of $R$ sets the stage for the magnetic ground state instability observed along this series.

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 pins down matching Cmmm' structures with +-+- stacking and a-moments for both Gd and Tb compounds, a clear contrast to Yb, but the claim that b-expansion stabilizes the stacking is an unmodeled inference.

read the letter

The main new result is the resonant x-ray determination that GdNiSi3 and TbNiSi3 share the same magnetic structure below their Neel points: Cmmm' symmetry, ferromagnetic ac planes stacked in +-+- antiferromagnetic order, and rare-earth moments along a. This differs from the +--+ stacking and b-directed moments in YbNiSi3, so the work documents a sign change in the second-neighbor interplane coupling across the series. The b-axis magnetoelastic expansion below TN is also measured and offered as the selector for that stacking pattern. The experimental structure solution itself is the solid part; single-crystal resonant x-ray intensities are used to fix the propagation vector and moment direction, which is the kind of concrete data the subfield needs to interpret the metamagnetic transitions. The soft spot is the causal step. The abstract concludes that the observed expansion stabilizes the +-+- pattern, yet no exchange-parameter calculations or energy comparisons versus lattice spacing are supplied to show that a ~0.1% change is sufficient to flip the sign or that other R-dependent terms are secondary. The link remains an inference rather than a tested claim. This paper is for readers already working on the RNiSi3 series or related rare-earth intermetallics who need the actual zero-field structures. A specialist will get direct value from the reported space group and moment directions; a general reader will not. The experimental claims are specific enough to merit peer review even if the discussion section would benefit from quantitative modeling of the exchange versus lattice parameter.

Referee Report

2 major / 1 minor

Summary. The manuscript reports resonant x-ray magnetic diffraction experiments performed on single crystals of GdNiSi3 and TbNiSi3 at zero field. Both compounds order below TN = 22.2 K and 33.2 K into the same magnetic structure (space group Cmmm') consisting of ferromagnetic ac planes stacked antiferromagnetically in a +-+- pattern with rare-earth moments aligned along a. This structure is contrasted with the +--+ stacking and b-directed moments reported for YbNiSi3. The b-axis lattice parameter exhibits magnetoelastic expansion below TN, which the authors interpret as stabilizing the +-+- pattern through tuning of the second-neighbor interplane exchange.

Significance. If the structure solutions hold, the work supplies concrete experimental anchors for the evolution of magnetic interactions across the RNiSi3 series, showing that a modest change in rare-earth size can reverse the sign of a key interplane coupling. The reported magnetoelastic response adds direct evidence of lattice-magnetic coupling in these compounds. The resonant x-ray approach is well suited to distinguishing the proposed structures.

major comments (2)

[Abstract] Abstract, final sentence: the assertion that b-axis magnetoelastic expansion stabilizes the +-+- stacking (via sign reversal of the second-neighbor coupling) is presented as a conclusion, yet no calculation of J2(R) versus lattice parameter, total-energy comparison, or estimate of the energy scale associated with the ~0.1% expansion is supplied; this interpretive step is load-bearing for the claim that lattice expansion is the dominant selector.
[Results (magnetic structure determination)] Results section describing the resonant x-ray structure solution: the assignment of Cmmm', the +-+- stacking, and the moment direction along a rests on diffraction intensities, but the manuscript supplies neither the measured intensities (or rocking curves), error bars, polarization analysis, nor any refinement statistics (R-factor, goodness-of-fit) that would allow independent verification of the structure that underpins the contrast with YbNiSi3.

minor comments (1)

[Abstract and Results] The magnetic space-group notation Cmmm' is used without explicit reference to the International Tables or a description of the primed operations; a short clarification would aid readers unfamiliar with magnetic crystallography conventions.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their positive evaluation of the significance of our work and for the detailed comments, which help clarify the presentation of our results. We respond to each major comment below.

read point-by-point responses

Referee: [Abstract] Abstract, final sentence: the assertion that b-axis magnetoelastic expansion stabilizes the +-+- stacking (via sign reversal of the second-neighbor coupling) is presented as a conclusion, yet no calculation of J2(R) versus lattice parameter, total-energy comparison, or estimate of the energy scale associated with the ~0.1% expansion is supplied; this interpretive step is load-bearing for the claim that lattice expansion is the dominant selector.

Authors: We agree that the manuscript presents an interpretive conclusion without supporting calculations of exchange constants or energy scales. The suggestion arises from the direct experimental observation of b-axis expansion below TN in the two compounds, together with the contrast to the different stacking and moment direction in YbNiSi3. In the revised manuscript we will change the abstract wording from 'pointing to the conclusion' to 'suggesting that' the expansion stabilizes the +-+- pattern, and we will add a short note in the discussion that quantitative modeling of J2 under lattice strain lies outside the scope of this experimental study. revision: yes
Referee: [Results (magnetic structure determination)] Results section describing the resonant x-ray structure solution: the assignment of Cmmm', the +-+- stacking, and the moment direction along a rests on diffraction intensities, but the manuscript supplies neither the measured intensities (or rocking curves), error bars, polarization analysis, nor any refinement statistics (R-factor, goodness-of-fit) that would allow independent verification of the structure that underpins the contrast with YbNiSi3.

Authors: The structure assignment is based on the observed positions, systematic absences, and relative intensities of the resonant magnetic reflections, as shown in the figures and described in the text. To permit independent verification we will add to the revised manuscript a table of representative magnetic reflections together with their integrated intensities, estimated uncertainties, and the intensities calculated for the Cmmm' model; the associated R-factor and goodness-of-fit will also be stated. Polarization analysis was not performed because the strong resonant enhancement at the Gd and Tb L3 edges, combined with the temperature dependence below TN, already distinguishes magnetic from charge scattering. revision: yes

Circularity Check

0 steps flagged

No circularity: experimental structure solution with interpretive conclusion

full rationale

The paper determines magnetic structures via resonant x-ray diffraction intensities on single crystals, yielding the Cmmm' space group, +-+- stacking, and moments along a for both GdNiSi3 and TbNiSi3. This is compared to prior YbNiSi3 results (external citation) and linked interpretively to observed b-axis magnetoelastic expansion below TN. No equations, parameter fits, self-citations, or ansatzes are present that reduce any claim to its own inputs by construction. The causal inference about lattice expansion selecting the stacking pattern is stated as a conclusion without quantitative modeling, but this is not a derivation that loops back on itself. The work is self-contained against external diffraction data.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

Claims rest on standard assumptions of resonant x-ray magnetic diffraction rather than new parameters or entities; no free parameters or invented entities are introduced.

axioms (1)

domain assumption Resonant x-ray magnetic diffraction peaks can be uniquely indexed to a single magnetic structure model without significant ambiguity from multiple scattering or domain effects.
Invoked implicitly when the abstract states the structure is determined from the diffraction data.

pith-pipeline@v0.9.0 · 5863 in / 1335 out tokens · 28186 ms · 2026-05-24T17:17:44.771843+00:00 · methodology

discussion (0)

Reference graph

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Durivault, F

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