Magnetic phase transitions and non-collinear spin structures in Weyl semimetal materials RAlSi (R=Ce, Nd, Sm)

Magnetic Weyl semimetals RAlSi (R = rare-earth) have a non-centrosymmetric crystal structure and a magnetic order, which makes them break both inversion symmetry and time-reversal symmetry. We focus on this material family and study their magnetic properties and spin structures using magnetic x-rays, susceptibility, neutron scattering, and heat capacity. Combining the experimental findings with first-principle DFT calculations, we find a gradual softening of the magnetic anisotropy from cerium to samarium compound. In parallel, the magnetic structures evolves from a commensurate in-plane order in CeAlSi, to an incommensurate out-of-plane order in NdAlSi, and a seemingly spiral order in SmAlSi. We will discuss the potential connection between these magnetic structures and the topological character of the band structure.