Rice University researchers report that YbMnBi₂, a compound containing rare-earth ytterbium, retains directionally organized spin fluctuations after its conventional antiferromagnetic order disappears. The team calls this a dynamic spin nematic state: it resembles a liquid crystal in how it favors certain directions, but it is not a literal liquid. The findings, published in Physical Review X on October 1, 2026, may also help explain unusual Hall and Nernst signals in the material.
What is a magnetic liquid crystal?
A spin nematic state has directional organization in the way spins behave without the conventional long-range magnetic order in which spins settle into a regular, ordered pattern. The liquid-crystal comparison describes this directional preference: like molecules in a liquid crystal, the fluctuating spins can favor certain orientations while remaining dynamic. It does not mean the solid becomes a liquid.
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In YbMnBi₂, the reported change is in low-energy spin excitations within the tetragonal plane. Above the antiferromagnetic transition, the excitations become anisotropic—more pronounced along some directions than others—rather than isotropic. The authors describe this as dynamic spin nematic behavior.
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The team used polarized neutron scattering to study YbMnBi₂ and CaMnBi₂. Both compounds are c-axis-aligned collinear antiferromagnets below their respective Néel temperatures, the temperatures at which antiferromagnetic order sets in. The measurements then tracked spin excitations above those transitions. The Physical Review X paper reports that as YbMnBi₂ cooled from 450 K toward its transition, its low-energy excitations changed from isotropic to anisotropic, with a dynamic spin nematic phase appearing around 400 K.
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The paper gives approximate Néel temperatures of 290 K for YbMnBi₂ and 270 K for CaMnBi₂. These are reported temperatures for the studied compounds, not precise operating thresholds for a device or a guarantee that every sample will show an identical transition.
Why compare YbMnBi₂ with CaMnBi₂?
CaMnBi₂ substitutes nonmagnetic calcium for ytterbium, giving the researchers a comparison for assessing ytterbium’s role. Above its ordering temperature, CaMnBi₂ showed isotropic paramagnetic scattering and no reported spin nematic phase. In contrast, YbMnBi₂ showed directional anisotropy in its low-energy excitations. This contrast supports a role for ytterbium in the behavior, though it does not by itself establish every microscopic detail of the interaction.
| Compound | Behavior above its antiferromagnetic transition | Approximate Néel temperature |
|---|---|---|
| YbMnBi₂ | Low-energy excitations become anisotropic; dynamic spin nematic behavior is reported around 400 K during cooling from 450 K. Physical Review X | 290 K. Physical Review X |
| CaMnBi₂ | Isotropic paramagnetic scattering; no spin nematic phase is reported. Physical Review X | 270 K. Physical Review X |
How could the spin state affect the Hall effect?
The authors propose that an in-plane magnetic field couples to Yb³⁺ moments, which interact with the dynamic manganese spin nematic state. In their proposed mechanism, that interaction induces scalar spin chirality—a handed arrangement involving spins—which can affect how electrons move through the material and produce anomalous Hall and anomalous Nernst responses. The paper presents this as an interpretation supported by measurements and symmetry analysis, not as a settled explanation for anomalous Hall effects in general.
The neutron measurements found the manganese spins to be essentially collinear. That result does not support a canted- or tilted-spin explanation for the bulk material under the reported conditions, prompting the authors to consider the chirality mechanism instead. It should not be generalized to every possible sample condition or magnetic material. Rice’s account of the work quotes graduate co-first author Yaofeng Xie explaining that the measurements motivated the search for another explanation, and Professor Pengcheng Dai describing the proposed interaction between ytterbium moments and manganese fluctuations. Rice University’s October 2, 2026 report provides the account and quotations.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What the finding does—and does not—establish
The result is a materials-physics finding about how magnetic fluctuations can remain directionally organized above conventional magnetic ordering. The authors identify spintronics as a possible research direction, but the study does not demonstrate a device, product, or near-term application. Its significance is a proposed route for understanding unusual electronic responses in this compound, rather than evidence that a practical technology is ready.
The primary study is by Yaofeng Xie, Sijie Xu, Yu Pan, Taekoo Oh, Tingjun Zhang, and coauthors, with Naoto Nagaosa and Pengcheng Dai as corresponding authors. It appeared as “Spin Nematic Liquid Crystal and Scalar Spin Chirality in Tetragonal Lattice” in Physical Review X 16, 041001 (2026). The journal’s Volume 16, Issue 4 page lists the publication issue.
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