75As NMR study of the ternary iron arsenide BaFe2As2
  We report 75As-NMR measurements of the ternary iron arsenide BaFe2As2. 75As-NMR spectra clearly revealed that magnetic transition occurs at around 131 K in our samples, which corresponds to the emergence of spin density wave. Temperature dependence of the internal magnetic field suggests that the transition is likely of the first order. The critical-slowing-down phenomenon in the spin-lattice relaxation rate 1/T1 is not pronounced in this material. 
H. Fukazawa, K. Hirayama, K. Kondo, T. Yamazaki, Y. Kohori, N.   Takeshita, K. Miyazawa, H. Kito, H. Eisaki, A. Iyo