according to high-resolution magnetic x-ray scattering studies*

Superconductivity (SC) and the presence of ordered magnetic moments are in general antagonistic. Nonetheless, when a material is forced to accommodate these apparently incompatible order parameters it may exhibit subtle organization of these phases, in the form of "cryptomagnetism", FFLO, and spontaneous vortex states. In-depth experimental studies of such inhomogeneous phases have been rather challenging. Here we present a superconductor, RbEuFe₄As₄, with intertwined magnetic and superconducting properties ideally suited for magnetic x-ray scattering (MXS) studies. These diffraction studies revealed a long-range, fully coherent, and three-dimensionally ordered magnetic phase. This phase corresponds to a long-range order of Eu moments below the Néel temperature of ~15K. Magnetization measurements confirmed a full ionic moment of Eu coexisting with SC. MXS results of the magnetic structure, its correlation, and order parameter will be presented.