Coupling of fully symmetric As phonon to magnetism in <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi>Ba</mml:mi><mml:msub><mml:mrow><mml:mo>(</mml:mo><mml:msub><mml:mi>Fe</mml:mi><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mi>Au</mml:mi><mml:mi>x</mml:mi></mml:msub><mml:mo>)</mml:mo></mml:mrow><mml:mn>2</mml:mn></mml:msub></mml:mrow><mml:msub><mml:mi>As</mml:mi><mml:mn>2</mml:mn></mml:msub></mml:math>
Bibliographic record
Abstract
We study the coupling of the fully symmetric vibration mode of arsenic atoms to magnetism in a $\mathrm{Ba}{({\mathrm{Fe}}_{1\ensuremath{-}x}{\mathrm{Au}}_{x})}_{2}{\mathrm{As}}_{2}$ system by polarization-resolved Raman spectroscopy and neutron diffraction. In this system, there are two phase transitions: a tetragonal-to-orthorhombic structural phase transition at temperature ${T}_{S}$ and a magnetic phase transition into collinear spin-density wave (SDW) state at temperature ${T}_{N}$ ($\ensuremath{\le}{T}_{S}$). ${T}_{S}$ and ${T}_{N}$ almost coincide in the pristine compound, whereas they differ by as much as 8 K for compounds with dilute gold substitution for iron. Raman coupling to the ${A}_{g}$(As) phonon is forbidden for the $XY$ scattering geometry in the tetragonal phase above ${T}_{S}$, whereas it becomes allowed in the orthorhombic phase below ${T}_{S}$: The emerging mode's intensity indicates the lattice orthorhombicity. We find that upon cooling below ${T}_{S}$, first, weak ${A}_{g}$(As) phonon mode intensity appears in the $XY$ scattering geometry spectra; however, the mode's intensity is significantly enhanced in the magnetic phase below ${T}_{N}$. The ${A}_{g}$(As) phonon also shows an asymmetric line shape below ${T}_{N}$ and an anomalous linewidth broadening upon Au doping. We describe the anomalous behavior of the ${A}_{g}$(As) mode in the $XY$ scattering geometry using a Fano model involving the ${A}_{g}$(As) phonon interacting with the ${B}_{2g}({D}_{4h}$)-symmetry-like electron-hole continuum. We conclude that the temperature dependence of light coupling amplitude to the ${A}_{g}$(As) phonon follows the evolution of the magnetic order parameter $M(T)$. We propose that the intensity enhancement of the ${A}_{g}$(As) phonon in the $XY$ scattering geometry below ${T}_{N}$ is due to electronic anisotropy induced by the collinear SDW order parameter.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.002 | 0.002 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.001 |
| Insufficient payload (model declined to judge) | 0.061 | 0.006 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".