The electronic structure of ultrathin films of ␥Ј-Fe 4 N͑100͒ deposited on Cu͑100͒ has been characterized by a combination of photoelectron spectroscopies, scanning tunneling microscopy, and diffraction techniques. The comparison of the data with first-principles simulations sheds light on magnetic moments, type of bonding, and charge transfer. N atoms residing in the bulk or at the surface are found to be distinguishable. The ␥Ј-Fe 4 N͑100͒ surface is laterally heterogeneous and contains both

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... reas reconstructed with a p4gm͑2 ϫ 2͒ symmetry and bulklike terminated. The densities of states of the reconstructed and unreconstructed areas of the surface are obtained and compared with the experiment. Comparison with c͑2 ϫ 2͒N/Fe͑100͒ provides spectroscopic evidence that a subsurface excess of N drives the p4gm͑2 ϫ 2͒ reconstruction.