Magnetic field dependence of antiferromagnetism deep within a superconducting state in RbEuFe₄As₄ exploiting a charge-magnetic interference inherent in x-ray resonance

We present an application of a unique methodology to probe magnetic long-range order which is difficult to study using bulk magnetization when masked by a large diamagnetic signal from a superconducting (SC) state as in RbEuFe4As4 (RbEu1144) superconductor. In RbEu1144 SC state appears at ~37 K followed by an antiferromagnetic (AFM) transition at TN ~15 K characterized by a 4-unit-cell periodicity of Eu moments along c axis. We exploit an interference of charge and magnetic scattering of x-rays on resonance to observe field suppression of this AFM order as ferromagnetism is induced in the Eu sublattice under an increasing magnetic field applied along the basal plane. This method is free from detrimental effects of any diamagnetic signals from SC state. Due to a high magnetic contrast, we were able to observe hysteretic dichotomy of AFM and FM and determine trapped flux. Future potential to use this technique to image bulk distribution of vortex pinning using a diffraction contrast x-ray microscopy will be discussed.