Study of lattice distortion in Sr(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_{2}$ single crystals employing high-energy x-ray diffraction

For the iron arsenide family of superconductors, the interplay between structure, magnetism, and superconductivity is a major theme of research. Among $A$Fe$_{2}$As$_{2}$ ($A =$ Ca, Sr, Ba), a difference lies in the strength of magnetoelastic coupling: it is strongest in CaFe$_{2}$As$_{2}$ as indicated by strongly coupled first order phase transitions (structural and magnetic) and modest in BaFe$_{2}$As$_{2}$ in which the two phase transitions split with Co-substitution. Moreover, similar to the structural transition, the magnetic transition becomes second order with higher Co-concentration. SrFe$_{2}$As$_{2}$ shows intermediate behavior. Here we present a temperature-dependent study of the lattice distortion from tetragonal to orthorhombic in Sr(Fe$_{1-x}$Co$_{x})_{2}$As$_{2}$ single crystals through diffraction measurements using x-ray radiation of two energies: 8.047 keV and 100 keV. The lower energy probes a few micrometers down from the surface of the sample whereas the higher energy characterizes the bulk. Details of the lattice distortion obtained with these two probes will be discussed.\\[4pt] The work at Ames Laboratory was supported by US DOE, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Contract DE-AC02-07CH11358. This research used resources of Advanced Photon Source, a US DOE, Office of Science User Facility.