Synthesis, Structure and Magnetic Properties of New Layered   Iron-Oxychalcogenide Na2Fe2OSe2
  A new layered iron-oxychalcogenide Na2Fe2OSe2 has been synthesized and structurally characterized by powder X-ray diffraction. The structure is formed by alternate stacking of the newly discovered [Fe2OSe2] blocks and double layers of Na. Conductivity study shows that Na2Fe2OSe2 is a semiconductor with activation energy of 0.26 eV. Magnetic susceptibility and heat capacity measurements reveal an antiferromagnetic phase transition occurs at TN=73 K. A broad maximum of magnetic susceptibility and a slow decay of the specific heat above TN, arises as a result of two-dimensional short-range spin correlation. 
J. B. He, D. M. Wang, H. L. Shi, H. X. Yang, J. Q. Li, and G. F. Chen
cond-mat.str-el