The influence of the structural transition on magnetic fluctuations in   NaFeAs
  NaFeAs belongs to a class of Fe-based superconductors which parent compounds 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_S. It is interpreted as due to the stiffening of spin fluctuations along the in-plane magnetic hard axis due to the dxz and dyz orbital ordering. The appearance of anisotropic spin dynamics in the critical region above the T_S at T* offers a dynamic magnetic scattering mechanism for anisotropic electronic properties in the commonly referred "nematic phase". 
Juanjuan Liu, Jinchen Wang, Wei Luo, Jieming Sheng, Aifeng Wang,   Xianhui Chen, Sergey A. Danilkin, Wei Bao
cond-mat.supr-con