Vacancy-Induced Ferromagnetic Behavior in Antiferromagnetic NiO Nanoparticles: A Positron Annihilation Study
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Bibliographic record
Abstract
Pure NiO nanoparticles were subjected to isochronal thermal treatments in open air from 100 to 1000°C. X-ray diffraction (XRD) patterns indicate that all annealed samples exhibit a single phase of face-centered cubic (FCC) crystalline structure, obvious grain growth occurs only above 400°C and the average crystallite size increases from 20 to 80 nm. X-ray photoelectron spectroscopy (XPS) shows that only very few amount of Ni3 + and no impurity element have been found in the annealed samples. Positron annihilation measurements reveal that large number of Ni-vacancy defects exist in the grain surface region. These surface defects begin to recover after annealing above 400°C, and most of them are removed at 1000°C. Room temperature ferromagnetism is obviously observed for the samples annealed at 100 and 400°C. The saturation magnetization gradually decreases with the increase of the annealing temperature, and it almost disappears at 800 and 1000°C. The disappearance of ferromagnetism shows good coincidence with the recovery of Ni-vacancies. Our results suggest that the anomalous ferromagnetic behavior in NiO nanoparticles might be due to the surface Ni-vacancy defects instead of grain size effects.
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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 | 0.001 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.001 | 0.001 |
| Scholarly communication | 0.000 | 0.001 |
| 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 it