Columnar magnetic structure coupled with orthorhombic distortion in the antiferromagnetic iron arsenide SrFe$_2$As$_2$

TL;DR

This study uses neutron diffraction to reveal the magnetic structure of SrFe$_2$As$_2$, showing a strong coupling between its magnetic order and orthorhombic distortion below 205 K.

Contribution

It provides the first detailed determination of the magnetic propagation vector and magnetic structure in SrFe$_2$As$_2$, highlighting the coupling with structural distortion.

Findings

Magnetic reflections appear with orthorhombic distortion below 205 K.

Magnetic propagation vector is { extit{ extbf{q}}}=(1 0 1).

Fe magnetic moment is approximately 1.01 μ_B aligned along the a-axis.

Abstract

Neutron powder diffraction experiments were carried out on polycrystalline SrFe$_2$As$_2$ in order to determine the magnetic structure and its relationship with the crystallographic one. Below $T_0$=205 K, magnetic reflections appear simultaneously with the onset of the orthorhombic distortion. From a detailed Rietveld analysis, the magnetic propagation vector of SrFe$_2$As$_2$ is determined to be {\textit{\textbf{q}}}=(1 0 1); the coupling of Fe moments is antiferromagnetic along the longer $a$ direction within the Fe-As layer, and the interlayer coupling is antiferromagnetic as well. The size of the Fe magnetic moment is deduced to be 1.01(3) ${\mu}_{\rm B}$ with an orientation parallel to the a-axis. The temperature dependence of the magnetic moment shows excellent agreement with not only that of the muon precession frequency but also with that of the structural distortion, revealing the strong coupling of the columnar magnetic order and the structural distortion in SrFe$_2$As$_2$.