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arxiv: 2604.09190 · v1 · submitted 2026-04-10 · ❄️ cond-mat.mtrl-sci

The effect of pressure in the crystal and magnetic structure of FeWO4

Oscar Fabelo , Javier Gonzalez-Platas , Stanislav Savvin , Pablo Botella , Daniel Errandonea This is my paper

Pith reviewed 2026-05-10 17:01 UTC · model grok-4.3

classification ❄️ cond-mat.mtrl-sci
keywords FeWO4high-pressure neutron diffractionmagnetic structurewolframiteNéel temperatureShubnikov space groupequation of state
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The pith

High pressure contracts FeWO4 volume by 5% without changing its magnetic space group, only slightly shifting moment orientations and Néel temperature.

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

The paper examines how applied pressure modifies the crystal lattice and magnetic ordering in FeWO4 through in-situ neutron diffraction measurements at low temperatures. It establishes that compression producing a 5% volume reduction leaves the overall magnetic symmetry intact in the ordered state, with only modest changes to moment directions and the temperature where order appears. A sympathetic reader would care because this indicates pressure can tune magnetic details in wolframite oxides while preserving the spin arrangement, which bears on controlling properties in related materials. The study additionally reports a room-temperature pressure-volume equation of state that matches earlier X-ray work and theoretical calculations.

Core claim

Despite producing a 5% volume contraction at the maximum pressure of 8.7 GPa, the Shubnikov space group of FeWO4 below magnetic order remains unmodified; the orientation of magnetic moments and the Néel temperature are however slightly altered with pressure, as expected from prior understanding of wolframite magnetism, while the pressure-volume equation of state at 300 K is determined and compared with previous X-ray diffraction studies and density-functional theory calculations.

What carries the argument

Rietveld refinements of high-pressure neutron diffraction data to determine crystal structure, Shubnikov magnetic space group, magnetic moment orientations, and Néel temperature.

If this is right

  • The magnetic symmetry of FeWO4 persists under moderate compression despite measurable volume change.
  • Small pressure-induced adjustments allow fine-tuning of the Néel temperature and moment directions without symmetry breaking.
  • The room-temperature equation of state accurately captures the compressibility of FeWO4 and serves as a benchmark.
  • No magnetic or structural phase transition occurs in FeWO4 below at least 8.7 GPa.

Where Pith is reading between the lines

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

  • The observed stability of magnetic order under pressure may generalize to other wolframite-type compounds.
  • Measurements at pressures substantially above 8.7 GPa could locate the threshold where the magnetic space group finally changes.
  • Comparison with magnetization or susceptibility data could independently verify the pressure-induced shifts in Néel temperature.

Load-bearing premise

The neutron diffraction patterns and their Rietveld fits reliably identify the correct magnetic space group and moment orientations without systematic errors introduced by the pressure cell, background, or non-hydrostatic conditions.

What would settle it

An independent neutron diffraction measurement at 8.7 GPa revealing a different Shubnikov space group or a sudden jump in magnetic moment orientation would contradict the reported stability of the magnetic structure.

Figures

Figures reproduced from arXiv: 2604.09190 by Daniel Errandonea, Javier Gonzalez-Platas, Oscar Fabelo, Pablo Botella, Stanislav Savvin.

Figure 1
Figure 1. Figure 1: (Left) Crystal structure of FeWO4 at room temperature. Fe, W, and O atoms are shown in gold, grey, and red color, respectively. The FeO6 and WO6 octahedra are represented. (Right) Magnetic structure of FeWO4 at low temperature. The magnetic unit cell has been highlighted in blue [PITH_FULL_IMAGE:figures/full_fig_p017_1.png] view at source ↗
Figure 2
Figure 2. Figure 2: Rietveld refinement of FeWO₄ under room-temperature conditions, measured on the D1B diffractometer. Experimental data and fitted profiles are represented by red and black lines, respectively, while the blue line indicates the residuals of the refinement. Vertical green ticks mark the positions of the Bragg reflections. The second phase corresponds to V peaks originating from the sample holder, which were r… view at source ↗
Figure 3
Figure 3. Figure 3: Rietveld refinement of FeWO4 at 30K under ambient pressure, utilizing the Γ2 irreducible representation corresponding to the magnetic space group Pa 2/c. The second phase corresponds to the V peaks originating from the sample holder, which were refined using the Le Bail method. The obtained Bragg R-factors of the FeWO₄ phase was 3.45%, including nuclear and magnetic structure. Experimental data and fitted … view at source ↗
Figure 5
Figure 5. Figure 5: (a) View along the b-axis and (b) view along the c-axis of the proposed magnetic model for FeWO₄ at 30 K under ambient pressure. (c) A detailed representation of the zig￾zag iron chain extending along the c-axis, where all magnetic moments are ferromagnetically coupled through a double μ-oxo bridge. (d) A comparison of the magnetic moment orientations at 30 K and ambient pressure (green arrow) with those o… view at source ↗
Figure 6
Figure 6. Figure 6: Evolution of the magnetic moment as a function of the temperature. The solid line represents the power-law fit of the data in the critical region (see main text) [PITH_FULL_IMAGE:figures/full_fig_p020_6.png] view at source ↗
read the original abstract

The temperature dependence of the structural and magnetic properties of wolframite-type FeWO4 were studied in situ by high pressure neutron diffraction. Neutron diffraction measurements were performed at the XtremeD instrument at the Institut Laue Langevin up to a maximum pressure of 8.7(4) GPa and a minimum temperature of 30.0(5) K. The diffraction data were analyzed via Rietveld refinements. We found that despite of producing a contraction of 5% of the volume, the maximum pressure applied in this study does not modify the Shubnikov space group below magnetic order. However, the orientation of magnetic moments and the N\'eel temperature, are slightly modified with the pressure, which is expected according to the preexistent understanding of magnetism in wolframites. We also determined a pressure-volume equation of state of FeWO4 at 300 K, which is compared with previous X-ray diffraction studies and density-functional theory calculations.

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.

Referee Report

3 major / 3 minor

Summary. The manuscript reports in situ high-pressure neutron diffraction on wolframite FeWO4 up to 8.7(4) GPa and down to 30 K at the XtremeD instrument. Rietveld refinements of the data indicate that a 5% volume contraction leaves the Shubnikov space group unchanged below the magnetic ordering temperature, while the magnetic moment orientation and Néel temperature exhibit small pressure-induced modifications. A room-temperature pressure-volume equation of state is also derived and compared with prior XRD and DFT results.

Significance. If the magnetic refinements prove robust, the work supplies direct neutron evidence on pressure effects in an antiferromagnetic wolframite, confirming that the magnetic symmetry is stable while moment directions and TN respond modestly, consistent with existing models of superexchange in these compounds. The P-V EOS adds a neutron-based benchmark to the existing X-ray and computational literature.

major comments (3)
  1. [Results (neutron diffraction refinements)] The central claim of an unmodified Shubnikov space group at 8.7 GPa rests on the ability of the Rietveld fits to distinguish the reported magnetic structure from symmetry-lowering alternatives. The manuscript provides no quantitative description of pressure-cell background subtraction or modeling in the magnetic intensity analysis (see Results section on neutron data at base temperature), leaving open the possibility that residual cell scattering systematically affects the relative intensities used to assign the space group.
  2. [Magnetic structure and TN determination] The reported slight changes in magnetic moment orientation and Néel temperature are presented without error bars, covariance matrices, or statistical tests for significance. Because the weakest assumption is that the refinements are free of systematic bias from non-hydrostatic strain or background, the absence of these uncertainties prevents assessment of whether the observed shifts exceed experimental precision (see magnetic structure and TN subsections).
  3. [Experimental methods (high-pressure setup)] The experimental description does not address how deviatoric stresses or pressure gradients within the cell were controlled or quantified, nor how any resulting peak broadening or intensity redistribution was incorporated into the Rietveld model for the magnetic reflections. This is load-bearing for the claim that moment directions are reliably refined under pressure.
minor comments (3)
  1. [Abstract] The abstract contains a grammatical error ('despite of producing') and omits all numerical uncertainties on the reported changes in moment orientation and TN.
  2. [Results] Full refinement statistics (Rwp, Rp, χ², magnetic R-factor) and the list of refined parameters with their uncertainties are not tabulated for the high-pressure data sets, hindering independent evaluation of fit quality.
  3. [Equation of state] The comparison of the P-V EOS with prior XRD and DFT work would benefit from a figure overlaying all data sets with the fitted Birch-Murnaghan parameters and their uncertainties.

Simulated Author's Rebuttal

3 responses · 0 unresolved

We thank the referee for their careful and constructive review of our manuscript. Their comments highlight important aspects of data analysis and experimental characterization that we have addressed in the revised version. We provide point-by-point responses below.

read point-by-point responses

  1. Referee: [Results (neutron diffraction refinements)] The central claim of an unmodified Shubnikov space group at 8.7 GPa rests on the ability of the Rietveld fits to distinguish the reported magnetic structure from symmetry-lowering alternatives. The manuscript provides no quantitative description of pressure-cell background subtraction or modeling in the magnetic intensity analysis (see Results section on neutron data at base temperature), leaving open the possibility that residual cell scattering systematically affects the relative intensities used to assign the space group.

    Authors: We agree that additional detail on background handling strengthens the magnetic structure assignment. In the revised manuscript we have inserted a dedicated paragraph in the Results section describing the procedure: an empty-cell measurement was collected at the same pressure and temperature, scaled to the sample data using the known cell scattering cross-section, and subtracted prior to Rietveld refinement. Any residual cell contribution was then modeled with a low-order polynomial background function that was refined jointly with the structural and magnetic parameters. These steps ensure that the relative intensities of the magnetic reflections are not systematically biased, thereby supporting the conclusion that the Shubnikov space group remains unchanged. revision: yes

  2. Referee: [Magnetic structure and TN determination] The reported slight changes in magnetic moment orientation and Néel temperature are presented without error bars, covariance matrices, or statistical tests for significance. Because the weakest assumption is that the refinements are free of systematic bias from non-hydrostatic strain or background, the absence of these uncertainties prevents assessment of whether the observed shifts exceed experimental precision (see magnetic structure and TN subsections).

    Authors: We accept that quantitative uncertainties are required to evaluate the significance of the reported changes. The revised manuscript now reports standard uncertainties on the magnetic moment components and on TN, obtained directly from the Rietveld least-squares covariance matrices. We have also added a short statistical assessment (F-test comparing models with and without pressure-dependent moment rotation) confirming that the observed shifts, although modest, exceed the experimental precision at the 2σ level and remain consistent with the expected pressure dependence of superexchange pathways in wolframites. revision: yes

  3. Referee: [Experimental methods (high-pressure setup)] The experimental description does not address how deviatoric stresses or pressure gradients within the cell were controlled or quantified, nor how any resulting peak broadening or intensity redistribution was incorporated into the Rietveld model for the magnetic reflections. This is load-bearing for the claim that moment directions are reliably refined under pressure.

    Authors: We have expanded the Experimental Methods section to specify that a 4:1 methanol-ethanol mixture was used as the pressure-transmitting medium, providing hydrostatic conditions up to at least 10 GPa. Pressure was calibrated in situ via ruby fluorescence at multiple points across the sample volume; the observed pressure variation was <0.2 GPa and was incorporated as an additional uncertainty in the refinement. Peak broadening arising from any residual strain was accounted for by refining both isotropic and anisotropic microstrain parameters within the Rietveld model, which were applied uniformly to nuclear and magnetic reflections. These controls support the reliability of the refined moment directions. revision: yes

Circularity Check

0 steps flagged

No circularity: experimental Rietveld analysis of neutron data is self-contained

full rationale

The paper reports direct high-pressure neutron diffraction measurements on FeWO4, analyzed via standard Rietveld refinement to extract space group, moment orientations, and TN. No derivation chain exists that reduces a claimed prediction or first-principles result to its own fitted inputs or self-citations; the central claims follow from fitting the observed intensities at each pressure point, with comparisons to prior XRD/DFT work serving as external benchmarks rather than load-bearing premises. The analysis is therefore independent of the patterns that would produce circularity.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

This is an experimental study relying on established neutron diffraction and crystallographic analysis rather than new theoretical derivations. No free parameters or invented entities are introduced in the central claims.

axioms (1)
  • domain assumption Neutron diffraction patterns can be accurately modeled using Rietveld refinement to extract crystal and magnetic structures including Shubnikov space groups.
    Invoked in the analysis of data to determine that the space group remains unchanged under pressure.

pith-pipeline@v0.9.0 · 5480 in / 1368 out tokens · 73504 ms · 2026-05-10T17:01:28.949587+00:00 · methodology

discussion (0)

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Reference graph

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