Collinear antiferromagnetism in trigonal SrMn$_{2}$As$_{2}$ revealed by single-crystal neutron diffraction

TL;DR

This study reveals that SrMn₂As₂ exhibits collinear antiferromagnetic order with Mn moments lying in the ab-plane, showing quasi-two-dimensional magnetic behavior, as determined by single-crystal neutron diffraction.

Contribution

The paper provides the first detailed magnetic structure of SrMn₂As₂, demonstrating collinear Néel AFM order with moments in the ab-plane and highlighting its quasi-two-dimensional magnetic properties.

Findings

Mn moments are in the ab-plane.

Collinear Néel AFM order with 180° alignment.

Quasi-two-dimensional AFM order observed.

Abstract

Fe pnictides and related materials have been a topic of intense research for understanding the complex interplay between magnetism and superconductivity. Here we report on the magnetic structure of SrMn$_{2}$As$_{2}$ that crystallizes in a trigonal structure ($P\bar{3}m1$) and undergoes an antiferromagnetic (AFM) transition at $T_{\textrm c}$ $= 118(2)$ K. The magnetic susceptibility remains nearly constant at temperatures $T \le T_{\textrm N}$ with $\textbf{H}\parallel \textbf{c}$ whereas it decreases significantly with $\textbf{H}\parallel \textbf{ab}$. This shows that the ordered Mn moments lie in the $\textbf{ab}$-plane instead of aligning along the $\textbf{c}$-axis as in tetragonal BaMn$_{2}$As$_{2}$. Single-crystal neutron diffraction measurements on SrMn$_{2}$As$_{2}$ demonstrate that the Mn moments are ordered in a collinear N\'{e}el AFM phase with $180^\circ$ AFM alignment between a moment and all nearest neighbor moments in the basal plane and also perpendicular to it. Moreover, quasi-two-dimensional AFM order is manifested in SrMn$_{2}$As$_{2}$ as evident from the temperature dependence of the order parameter.