Spin-State Transition in the Fe Pnictides
Bibliographic record
Abstract
We report an Fe $K\ensuremath{\beta}$ x-ray emission spectroscopy study of local magnetic moments in the rare-earth doped iron pnictide ${\mathrm{Ca}}_{1\ensuremath{-}x}{\mathrm{RE}}_{x}{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$ ($\mathrm{RE}=\mathrm{La}$, Pr, and Nd). In all samples studied the size of the Fe local moment is found to decrease significantly with temperature and goes from $\ensuremath{\sim}0.9{\ensuremath{\mu}}_{B}$ at $T=300\text{ }\text{ }\mathrm{K}$ to $\ensuremath{\sim}0.45{\ensuremath{\mu}}_{B}$ at $T=70\text{ }\text{ }\mathrm{K}$. In the collapsed tetragonal phase of Nd- and Pr-doped samples ($T<70\text{ }\text{ }\mathrm{K}$) the local moment is quenched, while the moment remains unchanged for the La-doped sample, which does not show lattice collapse. Our results show that ${\mathrm{Ca}}_{1\ensuremath{-}x}{\mathrm{RE}}_{x}{\mathrm{Fe}}_{2}{\mathrm{As}}_{2}$ ($\mathrm{RE}=\mathrm{Pr}$ and Nd) exhibits a spin-state transition and provide direct evidence for a nonmagnetic ${\mathrm{Fe}}^{2+}$ ion in the collapsed tetragonal phase; spin state as predicted by Yildirim. We argue that the gradual change of the spin state over a wide temperature range reveals the importance of multiorbital physics, in particular the competition between the crystal field split Fe $3d$ orbitals and the Hund's rule coupling.
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
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".