Ab initio density-functional theory in generalized gradient approximation is used to perform calculations on the magnetic structure of Mn thin films and Mn-Ni ordered surface alloys on Ni/Cu. For the Mn monolayer on Ni (001), Ni (011), and Ni (111), we found that the ground state corresponds to an antiferromagnetic coupling between Mn atoms. Ni subsurface atoms adjacent to Mn surface display two different values (0.26 μ B and 0.13 μ B) of the magnetic moment in the (111) crystallographic face. For the ordered Mn 0.5 Ni 0.5 monolayer on Ni a ferromagnetic configuration has been obtained. At variance, for the ordered Mn 0.5 Ni 0.5 two-layers thick on Ni an antiferromagnetic coupling between Mn atom nearest-neighboring positions are depicted for the (001) and (011) crystallographic faces whereas it is ferromagnetic for (111) one. Ni magnetic moments at surface alloy are killed (− 0.04 μ B). Mn overlayer and 1–2 …