We have performed high-resolution x-ray scattering measurements on single-crystal samples of Ba(Fe${}_{1-x}$Cr${}_x$)${}_2$As${}_2$ (0 $⩽$ x $⩽$ 0.335). These measurements examine the effect of Cr doping on the high-temperature tetragonal (I4/mmm) to low-temperature orthorhombic (Fmmm) structural phase transition of the parent compound BaFe${}_2$As${}_2$. Increasing Cr concentration is found to suppress the structural transition temperature ($T_s$) and reduce the magnitude of the orthorhombic strain ($\delta$). The doping dependence of the orthorhombic strain, combined with complementary measurements of the high-temperature magnetic susceptibility, suggests the presence of a magnetostructural crossover at $x\sim 0.05$. In particular, this crossover appears to mark a shift from strong to weak orthorhombicity and from predominantly itinerant to localized magnetic behavior.

• Received 30 June 2011

DOI:https://doi.org/10.1103/PhysRevB.85.054115