Neutron diffraction study on magnetic structures and transitions in Sr₂Cr₃As₂O₂

Sr₂Cr₃As₂O₂ is composed of alternating square-lattice CrO₂ and Cr₂As₂ stacking layers, where CrO₂ is isostructural to the CuO₂ building-block of cuprate high-Tc superconductors and Cr₂As₂ to Fe₂As₂ of Fe-based superconductors. Current interest in this material is raised by theoretic prediction of possible superconductivity. In this neutron powder diffraction study, we discovered that magnetic moments of Cr(II) ions in the Cr₂As₂ sublattice develop a C-type antiferromagnetic structure below 590 K, and the moments of Cr(I) in the CrO₂ sublattice form the La₂CuO₄-like antiferromagnetic order below 291 K. The staggered magnetic moment 2.19(4)μB/Cr(II) in the more itinerant Cr₂As₂ layer is smaller than 3.10(6)μB/Cr(I) in the more localized CrO₂ layer. Different from previous expectations, a spin-flop transition of the Cr(II) magnetic order observed at 291 K indicates a strong coupling between the CrO₂ and Cr₂As₂ magnetic subsystems.