Altermagnetism revealed by polarized neutrons in MnF$_2$
Bibliographic record
Abstract
Motivated by possible spintronics applications in antiferromagnets, it was recently observed that symmetry admits magnets that combine attractive features of both ferromagnets and antiferromagnets. These systems, dubbed altermagnets, have been the subject of intense study with direct spectroscopic evidence, from ARPES and RIXS, techniques reported in a handful of materials in the last year. Inelastic neutron scattering (INS) is one of the most powerful direct probes of magnetism and has recently been used to witness a splitting of magnon bands in MnTe that is compatible with altermagnetism although the nature and origin of the splitting remain to be fully characterized. However, the full power of neutron scattering for such systems comes from using polarized neutrons to measure the chirality of the magnon bands. Such a measurement provides a direct characterization of altermagnetism directly from the spin wave excitations. In this article, we present results on MnF$_2$ once thought to be an archetypal antiferromagnet. We present a polarized INS data that demonstrate the material is, in fact, altermagnetic. It had long been realized that the magnon bands in this material should have a weak splitting coming from the long-range dipolar coupling. Our data is the first to visualize this splitting directly. While the dipolar splitting on its own is not altermagnetic, using a domain biased sample, the data reveals a nonzero chirality in the neutron scattering cross section that reverses sign between the two magnon modes. It is this feature that clearly demonstrates altermagnetism in MnF$_2$. This finding highlights the potential for polarized INS to characterize altermagnets not least through its exquisite sensitivity to fine-structure in the magnon spectrum.
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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) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.001 | 0.002 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.001 | 0.001 |
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".