Quenching of Long Range Order and the Mn<sup>3+</sup> Ordered Moment in the Layered Antiferromagnet, Ba<sub><i>x</i></sub>Sr<sub>1–<i>x</i></sub>LaMnO<sub>4</sub>. A Polarized Neutron Scattering Study
Bibliographic record
Abstract
SrLaMnO 4 is a layered antiferromagnetic (AF) oxide with the tetragonal ( I 4/ mmm ) n = 1 Ruddlesden–Popper phase structure (also known as the K 2 NiF 4 structure) with T N = 128 K. Remarkably, substitution of Sr 2+ by Ba 2+, forming the solid solution Ba 1– x Sr x LaMnO 4, results in the destruction of long-range magnetic order and of the ordered moment on Mn 3+ for x > 0.35, although the effective paramagnetic moment remains unchanged, an unprecedented behavior for this class of magnetic materials. Four members, x = 0.0, 0.25, 0.35, and 1.0, have been studied using XYZ neutron polarization analysis which permits isolation of the magnetic, nuclear and nuclear spin components of the scattering and the measurement of the absolute value of the magnetic cross section. Data analysis is done using model independent reverse Monte Carlo methods (SPINVERT). The results for x = 0.0 (SrLaMnO 4 ), T > T N (128 K), show an asymmetric diffuse peak which evolves into resolution limited Bragg peaks below T N and a fully ordered AF ground state with a Mn 3+ moment of 3.06 μ B . For x = 0.25 the magnetic scattering below T N displays a remarkable phase separation—Bragg reflections coexisting with diffuse scattering. The ordered Mn 3+ moment is 1.1 μ B, much reduced from that obtained via unpolarized neutrons. There are no Bragg peaks for x = 0.35 at any measured temperature ( T > 3 K) but there is highly structured diffuse scattering indicating strong short-range order reminiscent of x = 0 and 0.25 above their respective transition temperatures. For x = 1.00 (BaLaMnO 4 ) the diffuse scattering roughly follows a paramagnetic form-factor indicating no short or long-range magnetic correlations. It is argued that the observed phenomena are due to a competition between AF and ferromagnetic (F) superexchange interactions for the 180° Mn 3+ –O–Mn 3+ geometry within the ab plane and that the changes in the local geometry of the Mn–O octahedron leads to reduction of the AF interaction with a likely enhancement of the F interaction with increasing Ba content, ultimately giving rise to a glassy ground state. Analysis of the diffuse magnetic components show clear 2D AF spin correlations above T N for x = 0.00, 0.25, and 0.35 with correlation lengths, ξ ∼ 14–7 Å and no spin correlations for x = 1.00.
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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".