The role of magnetism and disorder in superconductivity of gold-doped BaFe$_{\mathrm{2}}$As$_{\mathrm{2}}$ crystals

We present bulk magnetic and transport properties, and find structural and magnetic transitions, in order to construct the detailed T-x phase diagram for Ba(Fe$_{\mathrm{1-x}}$Au$_{\mathrm{x}})_{\mathrm{2}}$As$_{\mathrm{2}}$ single crystals [1]. The Au substitution into the FeAs-planes is only possible up to a small amount of \textasciitilde 3{\%}, probably due to the large size of gold. We find that 5$d$ is more effective in reducing magnetism in BaFe$_{\mathrm{2}}$As$_{\mathrm{2}}$ than its counter \textit{3d} Cu, and this relates to superconductivity. In this talk, we reveal more comprehensive neutron diffraction data in order to clarify some of the inferred $T_{N}$, $T_{S}$ points in our literature report [1]. New transmission electron microscopy results will be presented that sheds light on the role of chemical disorder for preventing high $T_{c}$ in these crystals. [1] L. Li et al., Phys. Rev. B 92, 094504 (2015).