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 increase upon cooling below the resolvable onset
of global orthorhombicity. This anisotropy in lattice coherence continues to build 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 thismaterial and that the development
of anisotropic lattice correlation lengths under strain is a possible origin for the high temperature transport
anisotropy in this compound.