Strain-activated structural anisotropy in BaFe2As2

TL;DR

This study investigates how uniaxial pressure induces anisotropic lattice changes in BaFe2As2, revealing strain-activated effects linked to magnetism and nematic behavior through neutron diffraction.

Contribution

It provides direct experimental evidence of strain-activated anisotropic lattice coherence and its connection to magnetoelastic coupling in BaFe2As2.

Findings

Strain causes anisotropic broadening of Bragg peaks below orthorhombic transition.

Lattice anisotropy diverges until antiferromagnetic order sets in.

Magnetism and magnetoelastic effects drive the strain response.

Abstract

High-resolution single crystal neutron diffraction measurements are presented probing the magnetostructural response to uniaxial pressure in the iron pnictide parent system BaFe2As2. Scattering data reveal a strain-activated, anisotropic broadening of nuclear Bragg reflections, which increases upon cooling below the resolvable onset of global orthorhombicity. This anisotropy in lattice coherence continues to diverge until a lower temperature scale---the first-order onset of antiferromagnetism---is reached. Our data suggest that antiferromagnetism and strong magnetoelastic coupling drive the strain-activated lattice response in this material and that the development of anisotropic lattice coherence under strain is the physical origin for the anomalous nematic anisotropy in this compound.