Neutron Scattering Measurements of Spatially Anisotropic Magnetic   Exchange Interactions in Semiconducting K0.85Fe1.54Se2 (TN=280 K)
  We use neutron scattering to study the spin excitations associated with the stripe antiferromagnetic (AFM) order in semiconducting K$_{0.85}$Fe$_{1.54}$Se$_2$ ($T_N$=$280$ K). We show that the spin wave spectra can be accurately described by an effective Heisenberg Hamiltonian with highly anisotropic in-plane couplings at $T$= $5$ K. At high temperature ($T$= $300$ K) above $T_N$, short range magnetic correlation with anisotropic correlation lengths are observed. Our results suggest that, despite the dramatic difference in the Fermi surface topology, the in-plane anisotropic magnetic couplings are a fundamental property of the iron based compounds; this implies that their antiferromagnetism may originate from local strong correlation effects rather than weak coupling Fermi surface nesting. 
Jun Zhao, Yao Shen, R. J. Birgeneau, Miao Gao, Zhong-Yi Lu, D.-H. Lee,   X. Z. Lu, H. J. Xiang, D. L. Abernathy, and Y. Zhao
cond-mat.supr-con cond-mat.str-el