NMR Search for the Spin Nematic State in LaFeAsO Single Crystal
  We report a 75-As single crystal NMR investigation of LaFeAsO, the parent phase of a pnictide high Tc superconductor. We demonstrate that spin dynamics develop a strong two-fold anisotropy within each orthorhombic domain below the tetragonal-orthorhombic structural phase transition at T[TO]~156 K. This intermediate state with a dynamical breaking of the rotational symmetry freezes progressively into a spin density wave (SDW) below T[SDW]~142 K. Our findings are consistent with the presence of a spin nematic state below T[TO] with an incipient magnetic order. 
M. Fu, D. A. Torchetti, T. Imai, F. L. Ning, J.-Q. Yan and A. S. Sefat
cond-mat.supr-con cond-mat.str-el