Long-range magnetic order in the 5<i>d</i><sup>2</sup>double perovskite Ba<sub>2</sub>CaOsO<sub>6</sub>: comparison with spin-disordered Ba<sub>2</sub>YReO<sub>6</sub>
Bibliographic record
Abstract
The B-site ordered double perovskite Ba2CaOsO6 was studied by dc magnetic susceptibility, powder neutron diffraction and muon spin relaxation methods. The lattice parameter is a = 8.3619(6) Å at 280 K and cubic symmetry [Formula: see text] is retained to 3.5 K with a = 8.3462(7) Å. Curie-Weiss susceptibility behaviour is observed for T > 100 K and the derived constants are C = 0.3361(3) emu K mol(-1) and ΘCW = -156.2(3) K, in excellent agreement with literature values. This Curie constant is much smaller than the spin-only value of 1.00 emu K mol(-1) for a 5d(2) Os(6+) configuration, indicating a major influence of spin-orbit coupling. Previous studies had detected both susceptibility and heat capacity anomalies near 50 K but no definitive conclusion was drawn concerning the nature of the ground state. While no ordered Os moment could be detected by powder neutron diffraction, muon spin relaxation (µSR) data show clear long-lived oscillations indicative of a continuous transition to long-range magnetic order below TC = 50 K. An estimate of the ordered moment on Os(6+) is ∼ 0.2 μB, based upon a comparison with µSR data for Ba2YRuO6 with a known ordered moment of 2.2 μB. These results are compared with those for isostructural Ba2YReO6 which contains Re(5+), also 5d(2), and has a nearly identical unit cell constant, a = 8.36278(2) Å-a structural doppelgänger. In contrast, Ba2YReO6 shows ΘCW = - 616 K, and a complex spin-disordered and, ultimately, spin-frozen ground state below 50 K, indicating a much higher level of geometric frustration than in Ba2CaOsO6. The results on these 5d(2) systems are compared to recent theory, which predicts a variety of ferromagnetic and antiferromagnetic ground states. In the case of Ba2CaOsO6, our data indicate that a complex four-sublattice magnetic structure is likely. This is in contrast to the spin-disordered ground state in Ba2YReO6, despite a lack of evidence for structural disorder, for which theory currently provides no clear explanation.
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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 | 0.000 |
| 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 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".