Electronic and magnetic phase diagram of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi mathvariant="normal">S</mml:mi> <mml:msub> <mml:mi mathvariant="normal">r</mml:mi> <mml:mn>2</mml:mn> </mml:msub> <mml:mi>Fe</mml:mi> <mml:msub> <mml:mi mathvariant="normal">O</mml:mi> <mml:mn>4</mml:mn> </mml:msub> </mml:mrow> </mml:math> at high pressure: A synchrotron Mössbauer study
Bibliographic record
Abstract
Transition metal (TM) oxides with high oxidation state TM ions exhibit a variety of unconventional electronic and magnetic states owing to electron correlations effects combined with highly covalent TM–O bonding. Here, we have studied the pressure dependence of electronic state and magnetism of the K 2 Ni F 4 -type iron(IV) oxide S r 2 Fe O 4 up to 89 GPa by temperature and magnetic field dependent energy-domain synchrotron Mössbauer spectroscopy and derived a ( P , T ) magnetic phase diagram. Considering also previous resistance studies [Rozenberg , ] several magnetic and electronic regimes with increasing pressure can be identified. Near 7 GPa, the insulating cycloidal antiferromagnetic low- P state is transformed into a semiconducting ferromagnetic state and the magnetic ordering temperature T m increases from 55 K at ambient pressure to about 100 K at 13 GPa. Between 18 and about 50 GPa the system is ferromagnetic and metallic (FMM) with a strong rise of T m to above room temperature (RT). Contrary to a recent theoretical study [Kazemi-Moridani , ], the FMM state is attributed to a high-spin t 2 g 3 e g 1 electronic state with itinerant e g coupled to more localized t 2 g electrons. Between 50 and 89 GPa a doublet with large quadrupole splitting in the RT Mössbauer spectra indicates a partial high-spin to low-spin ( t 2 g 4 ) transition leading to a decrease in T m again. The general features of the ( P , T ) phase diagram of S r 2 Fe O 4 are comparable to those of other simple and A -site ordered iron(IV) perovskite-related oxides with the peculiarity that S r 2 Fe O 4 adopts an insulating state without charge disproportionation of F e 4 + in the low- P region. The high-pressure behavior of S r 2 Fe O 4 and other iron(IV) oxides may be relevant for exploring the role of Hund's physics in multiorbital systems and contributing to the understanding of the electronic situation in unconventional superconductors such as L a 3
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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) | 0.010 | 0.001 |
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".