Competing ordering phenomena in the intermetallic topological magnets Eu(Ga_1-xAl_x)₄

Eu(Ga_1–x Al_x)₄ are centrosymmetric crystals that have recently been identified as candidates to stabilise topologically non-trivial magnetic phases, such as skyrmion lattices. We present a high-resolution resonant magnetic x-ray scattering study on this family of materials that provides new details of the complex coupling between the electronic ordering phenomena. Our results unambiguously demonstrate that in EuGa₂Al₂ a spin density wave forms with moments aligned perpendicular to the direction of the propagation vector below 19.5 K, and upon further cooling below 15 K, a cycloid with moments in the ab plane. We show that concomitant with the onset of the spin density wave is the suppression of the charge density wave order, indicative of a coupling between the localised 4f electrons and itinerant electron density. Furthermore we demonstrate that the charge density wave order breaks the four-fold symmetry present in the I4/mmm crystal structure, thus declassifying these systems as square-net magnets.