Effect of uniaxial strain on the structural and magnetic phase   transitions in BaFe$_2$As$_2$
  We report neutron scattering experiments probing the influence of uniaxial strain on both the magnetic and structural order parameters in the parent iron pnictide compound, BaFe$_2$As$_2$. Our data show that modest strain fields along the in-plane orthorhombic b-axis can affect significant changes in phase behavior simultaneous to the removal of structural twinning effects. As a result, we demonstrate in BaFe$_2$As$_2$ samples detwinned via uniaxial strain that the in-plane C$_4$ symmetry is broken by \textit{both} the structural lattice distortion \textit{and} long-range spin ordering at temperatures far above the nominal (strain-free), phase transition temperatures. Surprising changes in the magnetic order parameter of this system under relatively small strain fields also suggest the inherent presence of magnetic domains fluctuating above the strain-free ordering temperature in this material. 
Chetan Dhital, Z. Yamani, Wei Tian, J. Zeretsky, A. S. Sefat, Ziqiang   Wang, R. J. Birgeneau, and Stephen D. Wilson
cond-mat.supr-con cond-mat.str-el