UC Berkeley

High-resolution single crystal neutron diffraction measurements are presented probing the magnetostructural response to uniaxial pressure in the iron pnictide parent system BaFe2s2. 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 this material and that the development of anisotropic lattice correlation lengths under strain is a possible origin for the high temperature transport anisotropy in this compound.