Neutron diffraction study on magnetic structures and transitions in Sr2Cr3As2O2

TL;DR

This neutron diffraction study reveals complex magnetic ordering in Sr2Cr3As2O2, showing antiferromagnetic transitions in both CrO2 and Cr2As2 layers and a strong coupling between them, with potential implications for superconductivity.

Contribution

The paper provides the first detailed neutron diffraction analysis of magnetic structures and transitions in Sr2Cr3As2O2, highlighting the coupling between its layered magnetic subsystems.

Findings

Cr(II) ions in Cr2As2 layer develop C-type antiferromagnetic order below 590 K.

Cr(I) ions in CrO2 layer form La2CuO4-like antiferromagnetic order below 291 K.

A spin-flop transition at 291 K indicates strong coupling between magnetic subsystems.

Abstract

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){\mu} B /Cr(II) in the more itinerant Cr2As2 layer is smaller than 3.10(6){\mu}_B/Cr(I) in the more localized CrO2 layer. Different from previous expectation, 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.