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

Abstract

The parent compounds of recently discovered iron-arsenide superconductors, $A$Fe${}_2$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${}^o$-type structural domains in all parent compounds. Domains penetrate through the sample thickness in the $c$- direction and are not affected by crystal defects such as growth terraces. The domains form regular stripe patterns in the plane with a characteristic dimension of 10 to 50 $\mu m$. The direction of the stripes is fixed with respect to the tetragonal (100) and (010) directions but can change by 90${}^o$ on thermal cycling through the transition. This domain pattern may have profound implications for intrinsic disorder and anisotropy of iron arsenides.

arXiv commentOnline supplementary video is available at: http://www.cmpgroup.ameslab.gov/supermaglab/video/Pnictides.html

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