Disentangling Magnetic Order in EuIn₂As₂ with Resonant Soft X-ray Scattering

Zintl phase materials with cationic Eu have been a subject of great interest in recent years due to their ability to exhibit a variety of novel electronic phases. Recently, EuIn₂As₂ was proposed as a candidate axion insulator, a type of topological insulator exhibiting the topological magnetoelectric effect and axion field. The presence of an axion insulator requires the preservation of certain symmetries of the magnetic phase, so that the action remains quantized. Previous work has shown EuIn₂As₂ to exhibit broken helix magnetic order, a superposition of an A-type antiferromagnet and a helical antiferromagnet, which can be commensurate or incommensurate with the lattice. In this work, we use resonant soft X-ray scattering (RSXS) at the Eu M₅ edge to bring to light added complexities in the magnetic order of this material. Our work shows that several magnetic interactions coexist, each with different periodicity and origin, which are correlated with small changes in the c-axis lattice parameter and may be associated with deficiencies on the magnetic Eu²⁺ sites.