Direct imaging of the structural domains in the iron pnictides AFe2As2 (A=Ca,Sr,Ba)

The parent compounds of recently discovered iron-arsenide superconductors, AFe(2)As(2) with alkaline earth A=Ca,Sr,Ba, undergo simultaneous structural and magnetic phase transitions at a temperature T-SM. Using a combination of polarized light microscopy and spatially resolved high-energy synchrotron x-ray diffraction we show that the orthorhombic distortion leads to the formation of 45 degrees-type structural domains in all parent compounds. Domains penetrate through the sample thickness in the c direction and are not affected by crystal imperfections such as growth terraces. The domains form regular stripe patterns in the plane with a characteristic dimension of 10-50 mu m. The direction of the stripes is fixed with respect to the tetragonal (100) and (010) directions but can change by 90 degrees on thermal cycling through the transition. This domain pattern may have profound implications for intrinsic disorder and anisotropy of iron arsenides.