Magnetic ground states in the three <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi mathvariant="normal">O</mml:mi><mml:msup><mml:mrow><mml:mi mathvariant="normal">s</mml:mi></mml:mrow><mml:mrow><mml:mn>6</mml:mn><mml:mo>+</mml:mo></mml:mrow></mml:msup></mml:mrow></mml:math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>(</mml:mo><mml:mrow><mml:mn>5</mml:mn><mml:msup><mml:mi>d</mml:mi><mml:mn>2</mml:mn></mml:msup></mml:mrow><mml:mo>)</mml:mo></mml:math> double perovskites <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:mi mathvariant="normal">B</mml:mi><mml:msub><mml:mi mathvariant="normal">a</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:mi>M</mml:mi><mml:mi>Os</mml:mi><mml:msub><mml:mi mathvariant="normal">O</mml:mi><mml:mn>6</mml:mn></mml:msub></mml:mrow></mml:math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mo>(</mml:mo><mml:mrow><mml:mi>M</mml:mi><mml:mo>=</mml:mo><mml:mi>Mg</mml:mi><mml:mo>,</mml:mo><mml:mtext>Zn</mml:mtext><mml:mo>,</mml:mo><mml:mtext>and Cd</mml:mtext><mml:mo>)</mml:mo></mml:mrow></mml:math> from Néel order to its suppression
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Bibliographic record
Abstract
Three closely related double perovskites (DP) based on the $5{d}^{2}$ ion, $\mathrm{O}{\mathrm{s}}^{6+},\mathrm{B}{\mathrm{a}}_{2}M\mathrm{Os}{\mathrm{O}}_{6}$, with $M=\mathrm{Mg}$, Zn, and Cd have been prepared and characterized using x-ray (XRD) and neutron diffraction (ND), dc magnetization, heat capacity, and muon spin relaxation $(\ensuremath{\mu}\mathrm{SR})$ techniques. All three are cubic, Fm-$3m$, at ambient temperature from XRD with $\mathrm{\ensuremath{\Delta}}d/d\ensuremath{\sim}5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}$ resolution. For both $M=\mathrm{Mg}$ and Zn, ND data at 3.5 K and lower, $\mathrm{\ensuremath{\Delta}}d/d=2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}3}$, resolution show no signs of a distortion. The results are compared with the known DP material, $\mathrm{B}{\mathrm{a}}_{2}\mathrm{CaOs}{\mathrm{O}}_{6}$, which shows antiferromagnetic (AF) order below ${T}_{\mathrm{N}}=49\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ and a moderate frustration index, $f\ensuremath{\sim}4$, $(f=|{\ensuremath{\theta}}_{\mathrm{CW}}|/{T}_{\mathrm{N}})$, where ${\ensuremath{\theta}}_{\mathrm{CW}}$ is the Curie-Weiss temperature. $\mathrm{B}{\mathrm{a}}_{2}\mathrm{MgOs}{\mathrm{O}}_{6}$ with a unit cell constant ${a}_{0}=8.0757(1)\phantom{\rule{0.16em}{0ex}}\AA{}$, 3% smaller than for $\mathrm{B}{\mathrm{a}}_{2}\mathrm{CaOs}{\mathrm{O}}_{6}$, also shows N\'eel order below ${T}_{\mathrm{N}}=51\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ with $f\ensuremath{\sim}2$. However, $\mathrm{B}{\mathrm{a}}_{2}\mathrm{ZnOs}{\mathrm{O}}_{6},{a}_{0}=8.0975(1)\phantom{\rule{0.16em}{0ex}}\AA{}$, 0.27% larger than $\mathrm{B}{\mathrm{a}}_{2}\mathrm{MgOs}{\mathrm{O}}_{6}$, does not show N\'eel order from either heat capacity or $\ensuremath{\mu}\mathrm{SR}$ data. A zero field cooled/field cooled (ZFC/FC) irreversibility occurs near 30 K and a broad heat capacity anomaly is detected at a similar temperature. The $\ensuremath{\mu}\mathrm{SR}$ data are consistent with a weak spin ordering with an onset below 28 K but with a coexisting dynamic component. $\mathrm{B}{\mathrm{a}}_{2}\mathrm{CdOs}{\mathrm{O}}_{6}$ with ${a}_{0}=8.3190(1)\phantom{\rule{0.16em}{0ex}}\AA{}$, 0.5% smaller than $\mathrm{B}{\mathrm{a}}_{2}\mathrm{CaOs}{\mathrm{O}}_{6}$, shows no evidence for any type of order/spin freezing to 0.47 K from any of the measurement techniques applied. The results for $M=\mathrm{Zn}$ and Cd appear to lie outside of the mean field theory of Chen and Balents [Phys. Rev. B 84, 094420 (2011)] for cubic ${d}^{2}$ DP with strong spin orbit coupling, but $\mathrm{B}{\mathrm{a}}_{2}\mathrm{MgOs}{\mathrm{O}}_{6}$, along with $\mathrm{B}{\mathrm{a}}_{2}\mathrm{CaOs}{\mathrm{O}}_{6}$, is likely one of the three predicted AF phases. The remarkable contrast between the doppelg\"anger pairs $M=\mathrm{Mg}$/Zn and $M=\mathrm{Ca}$/Cd may be traceable to differences in electronic structure of the diamagnetic $M$ ions. All of the super-super exchange pathways in these DP materials involve Os--O--$M$--O--Os linkages.
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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 | 0.012 | 0.010 |
| Meta-epidemiology (narrow) | 0.008 | 0.015 |
| Meta-epidemiology (broad) | 0.003 | 0.014 |
| Bibliometrics | 0.004 | 0.010 |
| Science and technology studies | 0.012 | 0.012 |
| Scholarly communication | 0.012 | 0.012 |
| Open science | 0.017 | 0.017 |
| Research integrity | 0.014 | 0.014 |
| Insufficient payload (model declined to judge) | 0.535 | 0.021 |
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 it