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 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) | 0.000 | 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".