Local and Average Structures and Magnetic Properties of Sr<sub>2</sub>FeMnO<sub>5+<i>y</i></sub>, <i>y</i> = 0.0, 0.5. Comparisons with Ca<sub>2</sub>FeMnO<sub>5</sub> and the Effect of the A-Site Cation
Bibliographic record
Abstract
Sr(2)FeMnO(5+y) was synthesized under two different conditions, in air and in argon, both of which resulted in a cubic, Pm ̅3m, structure with no long-range ordering of oxygen vacancies. The unit cell constants were found to be a(0) = 3.89328(1) Å for argon (y = 0.0) and a(0) = 3.83075(3) Å for air (y = 0.5). In contrast, Ca(2)FeMnO(5) retains long-range brownmillerite oxygen vacancy ordering for either air or argon synthesis. Remarkably, Sr(2)FeMnO(5.0) oxidizes spontaneously in air at room temperature. A neutron pair distribution function (NPDF) study of Sr(2)FeMnO(5.0)(Ar) showed evidence for local, brownmillerite-like ordering of oxygen vacancies for short distances up to 5 Å. Mössbauer spectroscopy results indicate more than one Fe site for Sr(2)FeMnO(5+y)(Ar and air), consistent with the noncubic local structure found by NPDF analysis. The isomer shifts and quadrupole splittings in both air- and argon-synthesized materials are consistent with the 3+ oxidation state for Fe in sites with coordination number four or five. This is confirmed by an L-edge XANES study. Mn is almost entirely in the 3+ state for Sr(2)FeMnO(5.0)(Ar), whereas Mn(4+) is predominantly present for Sr(2)FeMnO(5.5)(air). Magnetic susceptibility data show zero-field-cooled/field-cooled (ZFC/FC) divergences near 50 K for the Ar sample and 25 K for the air sample, whereas Ca(2)FeMnO(5) is long-range G-type antiferromagnetically ordered at 407(2) K. Hyperfine magnetic splitting, observed in temperature-dependent Mössbauer measurements, indicates short-range magnetic correlations that persist up to 150 K for Sr(2)FeMnO(5.0)(Ar) and 100 K for Sr(2)FeMnO(5.5)(air), well above the ZFC/FC divergence temperatures. Neutron diffraction data confirm the absence of long-range magnetic ordering at room temperature and 4 K for Sr(2)FeMnO(5.0)(Ar) but indicate the presence of domains with short-range G-type order at 4 K with an average dimension of ∼50 Å (y = 0); thus, this material is actually a superparamagnet rather than a true spin glass. In sharp contrast, corresponding data for Sr(2)FeMnO(5.5)(air) show mainly a very weak magnetic Bragg peak, indicating that ∼4% of the sample has G-type antiferromagnetic ordering at 4 K.
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How this classification was reachedexpand
Full frame distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.003 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".