Limits for ordered magnetism in Pu from muon spin rotation spectroscopy
Bibliographic record
Abstract
We present $\ensuremath{\mu}\mathrm{SR}$ measurements on Pu metal which set stringent upper limits on the magnitude of the ordered moments ${\ensuremath{\mu}}_{\mathrm{ord}}$ in $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Pu}$ and $\ensuremath{\delta}$-stabilized Pu (alloyed with $4.3\phantom{\rule{0.3em}{0ex}}\mathrm{at}.%$ Ga). The magnitude of the low-temperature $(4\phantom{\rule{0.3em}{0ex}}\mathrm{K}<T<100--150\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ $\ensuremath{\mu}\mathrm{SR}$ rate in zero applied field is independent of temperature and consistent with nuclear dipolar broadening alone. The Knight shift in $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Pu}$ in $2\phantom{\rule{0.3em}{0ex}}\mathrm{T}$ applied field is also independent of temperature below about $100\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, but increases abruptly at higher temperatures, an effect likely caused by muon diffusion to paramagnetic impurities. A rough estimate for the muon hopping rate $1∕{\ensuremath{\tau}}_{h}$ at $150\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ in $\ensuremath{\alpha}\text{\ensuremath{-}}\mathrm{Pu}$ yields $1∕{\ensuremath{\tau}}_{h}\ensuremath{\approx}3\ifmmode\times\else\texttimes\fi{}{10}^{7}\phantom{\rule{0.3em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$; no estimate is yet obtained for $\ensuremath{\delta}\text{\ensuremath{-}}\mathrm{Pu}$. The principal results reported here are limits for ${\ensuremath{\mu}}_{\mathrm{ord}}$ in both $\ensuremath{\alpha}$- and $\ensuremath{\delta}\text{\ensuremath{-}}\mathrm{Pu}\ensuremath{\leqslant}{10}^{\ensuremath{-}3}{\ensuremath{\mu}}_{\mathrm{B}}$ at $\mathrm{T}\ensuremath{\cong}4\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. These limits are discussed in terms of recent models of the electronic properties of $\ensuremath{\delta}\text{\ensuremath{-}}\mathrm{Pu}$, where magnetism has been previously predicted. Our results are consistent with, but cannot unambiguously distinguish between, cases where the moments in $\ensuremath{\delta}\text{\ensuremath{-}}\mathrm{Pu}$ are essentially zero, possess very weak interatomic exchange, are reduced by hybridization, or are washed out by dynamical fluctuations.
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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 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.001 | 0.001 |
| 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 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".