The influence of the structural transition on magnetic fluctuations in NaFeAs*

NaFeAs belongs to a class of Fe-based superconductors which have parent compounds that show separated structural and magnetic transitions. Effects of the structural transition on spin dynamics therefore can be investigated separately from the magnetic transition. A plateau in dynamic spin response is observed in a critical region around the structural transition temperature $T_{\mathrm{S}}$. It is interpreted as being due to the stiffening of spin fluctuations along the in-plane magnetic hard axis due to the d$_{\mathrm{xz}}$ and d$_{\mathrm{yz}}$ orbital ordering. The appearance of anisotropic spin dynamics in the critical region above the $T_{\mathrm{S}}$ at $T$* offers a dynamic magnetic scattering mechanism for anisotropic electronic properties in the commonly referred `nematic phase'. Ref: J. Phys. Condens. Mater. 28 (2016) 27LT01