Magnetism of layered cobalt oxides investigated by muon spin rotation and relaxation
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Bibliographic record
Abstract
Muon spin rotation-relaxation $(\ensuremath{\mu}\mathrm{SR})$ spectroscopy has been used to investigate the magnetic properties of polycrystalline ${\mathrm{Ca}}_{3\ensuremath{-}x}{\mathrm{M}}_{x}{\mathrm{Co}}_{4}{\mathrm{O}}_{9}$ $(x<~0.5,M=\mathrm{Sr},\mathrm{Y},$ and Bi) and ${\mathrm{Na}}_{0.7}{\mathrm{CoO}}_{2}$ samples in the temperature range between 2.5 and 300 K. It was found that ${\mathrm{Ca}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{9}$ exhibits a magnetic transition at around ${T}_{c}=100\mathrm{K};$ at lower temperatures, two types of relaxation were observed using a weak transverse field $\ensuremath{\mu}\mathrm{SR}$ technique with $H=104\mathrm{Oe}:$ one with a fast relaxation rate ${\ensuremath{\lambda}}_{F}\ensuremath{\sim}10\ensuremath{\mu}{\mathrm{s}}^{\ensuremath{-}1}$ and the other with a slow ${\ensuremath{\lambda}}_{S}\ensuremath{\sim}0.1\ensuremath{\mu}{\mathrm{s}}^{\ensuremath{-}1}.$ Zero-field $\ensuremath{\mu}\mathrm{SR}$ measurements suggest the existence of an incommensurate spin-density-wave (SDW) state below ${T}_{c}$ (i.e., ${T}_{c}{=T}_{\mathrm{SDW}}),$ although a ferrimagnetic $M\ensuremath{-}H$ loop was observed by a dc susceptibility measurement below 19 K. The substitution of Y or Bi for Ca increased ${T}_{\mathrm{SDW}},$ while the substitution of Sr for Ca did not affect ${T}_{\mathrm{SDW}}.$ This indicates that the SDW transition depends strongly on the average valence of the Co ions. The related material ${\mathrm{Na}}_{0.7}{\mathrm{CoO}}_{2}$ showed no magnetic transitions below 30 K. Considering the difference between the crystal structures of ${\mathrm{Ca}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{9}$ and ${\mathrm{Na}}_{0.7}{\mathrm{CoO}}_{2},$ we suggest that Co ions in the rocksalt-type layers of ${\mathrm{Ca}}_{3}{\mathrm{Co}}_{4}{\mathrm{O}}_{9}$ are likely to play a significant role in inducing the SDW transition around 100 K.
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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 | 0.000 | 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 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 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 it