Scanning Tunneling Microscopy Study of Square Manganese Tetramers on   Mn3N2 (001)
  We have investigated the growth of antiferromagnetic Mn3N2(001) on MgO (001) by molecular beam epitaxy and scanning tunneling microscopy . The images show smooth terraces and atomic steps. On some of the terraces a unique and new reconstruction is seen, resolved as square Mn tetramers in a c(4x2) structural arrangement. Two domains of the tetramer reconstruction, rotated by 90$^\circ$ to each other, occur. A model is presented for this square Mn tetramer reconstruction, in which the Mn atoms of the tetramer layer belong to the Mn layer at the surface in the MnN-MnN-Mn stacking sequence. 
Rong Yang, Haiqiang Yang, and Arthur R. Smith