Magnetic excitations and interactions in the Weyl antiferromagnet NdAlSi

While magnetism can influence the creation and response of Weyl fermions in bulk systems, the influence of Weyl fermions on collective magnetism is a source of ongoing research. These materials present an opportunity to study fundamental interactions of exotic fermions in condensed matter systems, and have potential in future technological applications for enhanced storage capabilities due to their topological protection, versatility and tunability. Here we present elastic and inelastic neutron scattering data on Weyl semimetal NdAlSi for which we comprehensively model the spin structure and excitation spectrum. We highlight the presence of sign-changing (antiferromagnetic and ferromagnetic) exchange interactions, and the role of anisotropic Dzyaloshinskii-Moriya interactions that stabilize the observed helical magnetic order, having predictive power for isostructural magnets with exotic spin textures. Our work is the first experimental investigation into the magnetic excitations and microscopic interactions in this interesting class of noncentrosymmetric rare-earth Weyl magnets and serves to constrain the role of Weyl-mediated exchange.