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

TL;DR

This paper reanalyzes neutron diffraction data on NdAlSi, proposing that a fan magnetic structure, rather than a helical one, better explains the observed peaks, impacting the understanding of its topological properties.

Contribution

It challenges previous interpretations by suggesting a fan magnetic structure in NdAlSi instead of a helical one, influencing the understanding of its magnetic and topological behavior.

Findings

Fan magnetic structure fits diffraction data better than helical.

Helical and fan structures have different electromagnetic implications.

Re-examination prompts reconsideration of magnetic topology in NdAlSi.

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.