Note on the interpretation of magnetic diffraction in NdAlSi: helical or fan?

Abstract

We revisit the magnetic structure analysis reported in Nat. Mater. 20, 1650 (2021), which concluded that a Weyl semimetal candidate NdAlSi hosts a helical magnetic order. This conclusion was based on magnetic neutron diffraction peaks corresponding to modulation vectors ${\vec{k}}_{in}=(1/3,1/3,0)$ and ${\vec{k}}_{out}=(2/3,2/3,0)$, attributed to in-plane and out-of-plane components of the magnetic moments, respectively. Upon careful reanalysis, we suggest that a fan-type magnetic structure--rather than the helix--provides a more consistent interpretation of these data. Unlike a helical structure, fan structures do not exhibit handedness. The distinction has significant implications for interpreting the electromagnetic responses in this material. We believe that our suggestions motivate a re-examination of magnetic structures in NdAlSi and other tetragonal siblings, where the interplay between magnetism and topology is under active investigation.

arXiv comment3 pages, 2 figures, 1 table