Strong coupling between magnetic and structural order parameters in SrFe2As2

TL;DR

This study demonstrates a strong coupling between magnetic and structural phase transitions in SrFe2As2, revealing that both phenomena are closely linked and scale together, supported by experimental and theoretical evidence.

Contribution

It provides detailed experimental and theoretical evidence showing the intrinsic coupling between magnetic order and structural distortion in SrFe2As2.

Findings

First order transition at 205 K with orthorhombic distortion

Magnetic and structural order parameters are closely correlated

Magnetic moments scale with lattice distortion across related compounds

Abstract

X-ray and Neutron diffraction as well as muon spin relaxation and M\"ossbauer experiments performed on SrFe$_2$As$_2$ polycrystalls confirm a sharp first order transition at $T_0 = 205$,K corresponding to an orthorhombic phase distortion and to a columnar antiferromagnetic Fe ordering with a propagation vector (1,0,1), and a larger distortion and larger size of the ordered moment than reported for BaFe$_2$As$_2$. The structural and the magnetic order parameters present an remarkable similarity in their temperature dependence from $T_0$ down to low temperatures, showing that both phenomena are intimately connected. Accordingly, the size of the ordered Fe moments scale with the lattice distortion when going from SrFe$_2$As$_2$ to BaFe$_2$As$_2$. Full-potential band structure calculations confirm that the columnar magnetic order and the orthorhombic lattice distortion are intrinsically tied to each other.