Spin density waves and ground state helices in EuGa2.4Al1.6 [dataset]

The Eu(Ga1−xAlx )4 series is composed of centrosymmetric structures which exhibit a wide range of rich topological phenomena, including some members hosting magnetic skyrmions. In this letter, we investigate the previously unreported intermediate compound EuGa2.4Al1.6, which hosts two distinct phase transitions under zero applied magnetic field. We have used resonant elastic x-ray scattering with full linear polarization analysis to unambiguously determine the zero-field magnetic structures, which consist of a transition between a basal plane transverse spin density wave at higher temperatures into a noncollinear helical ground state. Furthermore, we demonstrate a phase coexistence regime below the transition and reveal an elliptically modulated helical magnetic structure emerging from wavevector splitting.