We alternately deposited Ni and Fe monatomic layers on Cu(001) single crystal substrates and also performed surfactant-mediated growth. FeNi films exhibited a large uniaxial magnetic anisotropy (K-u) of over 0.1 MJ/m(3) by using an oxygen or a gold surfactant, although K-u was almost zero without surfactants. Reflection high-energy electron diffraction and atomic force microscopy indicated surfactant effects of oxygen and gold. Synchrotron X-ray diffraction indicated a formation of an L1(o)-type ordered FeNi phase having a large K-u. We have considered that the surfactants enhanced layer-by-layer growth leading to the L1(o)-ordering by changing a diffusion scenario of Fe and Ni atoms. (C) 2016 Elsevier B.V. All rights reserved.