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In neodymium aluminium silicon (NdAlSi), researchers reported that neodymium spins form a spiral below about 14 K. They proposed that Weyl fermions help mediate the interactions behind that pattern—but the observed spiral and the proposed explanation are distinct findings, and the evidence does not establish NdAlSi as a Weyl magnet.
What happens to NdAlSi below about 14 K?
Neutron diffraction experiments at the National Institute of Standards and Technology, as described by Chemistry World on 1 September 2021, found neodymium spins disordered above about 14 K. Below that temperature, the spins spontaneously form a spiral arrangement.
The reported spiral wavelength is unrelated to the dimensions of NdAlSi’s crystal lattice. A magnetic spiral with a wavelength not set by the repeating lattice spacing is described as helimagnetic.
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Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Repair Windows errors before they cause bigger problemsFix Now →Scan for outdated or missing drivers - takes under a minuteDriver Scan →How might Weyl fermions relate to the spiral?
NdAlSi’s non-centrosymmetric crystal structure is the basis for describing it as a Weyl semimetal. The researchers proposed that Weyl fermions—exotic quasiparticles associated with this class of material—mediate interactions between neighboring neodymium atoms and contribute to the magnetic ordering. That is a proposed microscopic mechanism, not something the neutron diffraction result alone proves.
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Collin Broholm of Johns Hopkins University explained the proposed constraint this way: “In order to travel from site A to site B, [a Weyl fermion]’s spin has to point either from site A to site B or in the opposite detection. That very strongly constrains the nature of the interaction mediated between the neodymium atoms.” The report presents this spin-momentum-locking picture as a way the quasiparticles could shape interactions between the magnetic atoms.
Is NdAlSi a Weyl magnet?
That stronger label was not clearly established by the reported evidence. Physicist Zahid Hasan of Princeton University cautioned: “There is no clear evidence yet regarding the claim that this material is a Weyl magnet.” The distinction matters: the reported magnetic spiral is an experimental observation, while the role of Weyl fermions in producing it is an interpretation that remained unsettled in the 2021 report.
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Hasan described neutron scattering as an interesting way to explore magnetic Weyl semimetals and said further neutron experiments may reveal phenomena. Those comments reflect his view as reported by Chemistry World, rather than a claim that the Weyl-magnet interpretation had been confirmed.
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What study did the report describe?
Chemistry World identified the underlying 2021 study as J. Gaudet et al. in Nature Materials, DOI 10.1038/s41563-021-01062-8. The account available here is the publication’s explanatory report; its experimental details and quotations are attributed to that report.
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