Magnetism of coherent Co and Ni thin films on Cu(111) and Au(111) substrates: An ab initio study

We present an ab initio study of structural and magnetic properties of coherent Co and Ni thin films on Cu(111) and Au(111) substrates with thicknesses of up to 6 monolayers. All studied films on Cu(111) substrates prefer structures close their ground state (hcp for Co and fcc for Ni), whereas only the hcp stacking sequence has been found for both films on Au(111) substrates. All studied films exhibit instability of the first monolayer with respect to decomposition into 2-monolayer- or 3-monolayer-high islands, which is in agreement with experimental findings. All studied films are also ferromagnetic, nevertheless the Ni/Cu(111) films reduce their magnetic moments in the layer adjacent to the substrate due to a stronger Cu-Ni interaction at the interface. The magnetic anisotropy of a Co film does not depend on the film thickness: all the studied Co/Au(111) films exhibit a perpendicular magnetic anisotropy, whereas all the Co/Cu(111) films prefer in-plane magnetization. On the other hand, both Ni films change their preference for in-plane orientation of their easy axis to out-of-plane orientation at a critical thickness of 2 monolayers, however, the magnetic anisotropy energies for films thicker than 1 monolayer are smaller than 1 meV/Ni atom. These behaviors of magnetic anisotropy do not depend on the structure of the studied films.